Thank you for helping me.
The nextcloud.log file was 76 MB, so I went through it and copied out the first time it installed snap21. To fit it in the word limit I cut away all the similar error messages, and left one of each.
There were a few dozen of the following error:
{"reqId":"0o1bGP1bLATBUmcV4XgJ","level":4,"time":"2021-06-01T00:06:00+00:00","remoteAddr":"172.30.1.194","user":"classroom","app":"webdav","method":"PROPFIND","url":"/remote.php/dav/files/classroom/T's%20Manual-2020,%201st%20semester%E2%98%85","message":{"Exception":"OCA\\DAV\\Connector\\Sabre\\Exception\\Forbidden","Message":"No read permissions","Code":0,"Trace":[{"file":"/snap/nextcloud/28088/htdocs/3rdparty/sabre/dav/lib/DAV/Tree.php","line":200,"function":"getChildren","class":"OCA\\DAV\\Connector\\Sabre\\Directory","type":"->","args":[]},{"file":"/snap/nextcloud/28088/htdocs/3rdparty/sabre/dav/lib/DAV/Server.php","line":900,"function":"getChildren","class":"Sabre\\DAV\\Tree","type":"->","args":["files/classroom/T's Manual-2020, 1st semester\u2605"]},{"file":"/snap/nextcloud/28088/htdocs/3rdparty/sabre/dav/lib/DAV/Server.php","line":982,"function":"generatePathNodes","class":"Sabre\\DAV\\Server","type":"->","args":[{"__class__":"Sabre\\DAV\\PropFind"},[{"__class__":"Sabre\\DAV\\PropFind"},{"__class__":"OCA\\DAV\\Connector\\Sabre\\Directory"}]]},{"file":"/snap/nextcloud/28088/htdocs/3rdparty/sabre/dav/lib/DAV/Server.php","line":1661,"function":"getPropertiesIteratorForPath","class":"Sabre\\DAV\\Server","type":"->","args":["files/classroom/T's Manual-2020, 1st semester\u2605",["{DAV:}resourcetype","{DAV:}getlastmodified","{DAV:}getcontentlength","{DAV:}getetag","{http://owncloud.org/ns}id","And 5 more entries, set log level to debug to see all entries"],1]},{"file":"/snap/nextcloud/28088/htdocs/3rdparty/sabre/dav/lib/DAV/Server.php","line":1646,"function":"writeMultiStatus","class":"Sabre\\DAV\\Server","type":"->","args":[{"elementMap":[],"contextUri":"/remote.php/dav/","namespaceMap":{"DAV:":"d","http://sabredav.org/ns":"s","http://owncloud.org/ns":"oc","http://nextcloud.org/ns":"nc"},"classMap":[],"__class__":"Sabre\\Xml\\Writer"},{"__class__":"Generator"},false]},{"file":"/snap/nextcloud/28088/htdocs/3rdparty/sabre/dav/lib/DAV/CorePlugin.php","line":346,"function":"generateMultiStatus","class":"Sabre\\DAV\\Server","type":"->","args":[{"__class__":"Generator"},false]},{"file":"/snap/nextcloud/28088/htdocs/3rdparty/sabre/event/lib/WildcardEmitterTrait.php","line":89,"function":"httpPropFind","class":"Sabre\\DAV\\CorePlugin","type":"->","args":[{"__class__":"Sabre\\HTTP\\Request"},{"__class__":"Sabre\\HTTP\\Response"}]},{"file":"/snap/nextcloud/28088/htdocs/3rdparty/sabre/dav/lib/DAV/Server.php","line":472,"function":"emit","class":"Sabre\\DAV\\Server","type":"->","args":["method:PROPFIND",[{"__class__":"Sabre\\HTTP\\Request"},{"__class__":"Sabre\\HTTP\\Response"}]]},{"file":"/snap/nextcloud/28088/htdocs/3rdparty/sabre/dav/lib/DAV/Server.php","line":253,"function":"invokeMethod","class":"Sabre\\DAV\\Server","type":"->","args":[{"__class__":"Sabre\\HTTP\\Request"},{"__class__":"Sabre\\HTTP\\Response"}]},{"file":"/snap/nextcloud/28088/htdocs/3rdparty/sabre/dav/lib/DAV/Server.php","line":321,"function":"start","class":"Sabre\\DAV\\Server","type":"->","args":[]},{"file":"/snap/nextcloud/28088/htdocs/apps/dav/lib/Server.php","line":332,"function":"exec","class":"Sabre\\DAV\\Server","type":"->","args":[]},{"file":"/snap/nextcloud/28088/htdocs/apps/dav/appinfo/v2/remote.php","line":35,"function":"exec","class":"OCA\\DAV\\Server","type":"->","args":[]},{"file":"/snap/nextcloud/28088/htdocs/remote.php","line":167,"args":["/snap/nextcloud/28088/htdocs/apps/dav/appinfo/v2/remote.php"],"function":"require_once"}],"File":"/snap/nextcloud/28088/htdocs/apps/dav/lib/Connector/Sabre/Directory.php","Line":263,"CustomMessage":"--"},"userAgent":"Mozilla/5.0 (Windows) mirall/3.1.3stable-Win64 (build 20210218) (Nextcloud)","version":"21.0.1.1"}
And these:
{"reqId":"1rEyvwZaRRIBAYo0eYvW","level":2,"time":"2021-06-01T02:33:12+00:00","remoteAddr":"172.30.1.196","user":"--","app":"no app in context","method":"POST","url":"/index.php/login","message":"Login failed: ftksongdo (Remote IP: 172.30.1.196)","userAgent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.182 Safari/537.36 Edg/88.0.705.81","version":"21.0.1.1"}
{"reqId":"LxC5niQaXMqlBIKTeEFQ","level":2,"time":"2021-06-01T02:33:24+00:00","remoteAddr":"172.30.1.196","user":"--","app":"no app in context","method":"POST","url":"/index.php/login","message":"Login failed: ftksongdo (Remote IP: 172.30.1.196)","userAgent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.182 Safari/537.36 Edg/88.0.705.81","version":"21.0.1.1"}
{"reqId":"dFT1vSAtxlMtl4SmB1nw","level":2,"time":"2021-06-01T02:33:47+00:00","remoteAddr":"172.30.1.196","user":"--","app":"no app in context","method":"POST","url":"/index.php/login","message":"Login failed: ftksongdo (Remote IP: 172.30.1.196)","userAgent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.182 Safari/537.36 Edg/88.0.705.81","version":"21.0.1.1"}
{"reqId":"4J3wktHQiSau4Tefu8Ln","level":2,"time":"2021-06-01T02:35:52+00:00","remoteAddr":"172.30.1.196","user":"--","app":"core","method":"GET","url":"/remote.php/dav/files/ftksongdo/","message":"Login failed: 'ftksongdo' (Remote IP: '172.30.1.196')","userAgent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.182 Safari/537.36 Edg/88.0.705.81","version":"21.0.1.1"}
{"reqId":"u99e7Ctcj56d5y3hK9ss","level":2,"time":"2021-06-01T02:36:17+00:00","remoteAddr":"172.30.1.196","user":"--","app":"core","method":"GET","url":"/remote.php/dav/files/ftksongdo/","message":"Login failed: 'ftksongdo' (Remote IP: '172.30.1.196')","userAgent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.182 Safari/537.36 Edg/88.0.705.81","version":"21.0.1.1"}
{"reqId":"Ygoxn1MvXXdJjja2o6Wl","level":2,"time":"2021-06-01T02:36:40+00:00","remoteAddr":"172.30.1.196","user":"--","app":"core","method":"GET","url":"/remote.php/dav/files/ftksongdo/","message":"Login failed: 'ftksongdo' (Remote IP: '172.30.1.196')","userAgent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.182 Safari/537.36 Edg/88.0.705.81","version":"21.0.1.1"}
{"reqId":"22tNYbYUsms2OvAMljUK","level":2,"time":"2021-06-01T06:23:43+00:00","remoteAddr":"172.30.1.147","user":"--","app":"no app in context","method":"POST","url":"/index.php/login","message":"Login failed: ftkuser (Remote IP: 172.30.1.147)","userAgent":"Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.212 Safari/537.36","version":"21.0.1.1"}
And there must have been a hundred or more of these:
{"reqId":"jIaAl09CgNfPoKS7eFh6","level":4,"time":"2021-06-01T06:30:15+00:00","remoteAddr":"172.30.1.197","user":"classroom","app":"webdav","method":"GET","url":"/remote.php/dav/files/classroom/Documents%20(shared)/Naomi/%E2%98%85Naomi%20%EC%88%98%EC%97%85/Wise/Edu%20planet/TOEFL%20Primary%20MP3/Step%202/step%202%20book%203%20CD%20B/30%20%ED%8A%B8%EB%9E%99%2030.mp3","message":{"Exception":"RedisException","Message":"read error on connection to /tmp/sockets/redis.sock:0","Code":0,"Trace":[{"file":"/snap/nextcloud/28088/htdocs/lib/private/Memcache/Redis.php","line":169,"function":"watch","class":"Redis","type":"->","args":["0eb8081432e8ebf4790940bd5797ca1a/lockfiles/c57d9562cab4387ad86d32556039631d"]},{"file":"/snap/nextcloud/28088/htdocs/lib/private/Lock/MemcacheLockingProvider.php","line":105,"function":"cad","class":"OC\\Memcache\\Redis","type":"->","args":["files/c57d9562cab4387ad86d32556039631d",1]},{"file":"/snap/nextcloud/28088/htdocs/lib/private/Files/Storage/Common.php","line":784,"function":"releaseLock","class":"OC\\Lock\\MemcacheLockingProvider","type":"->","args":["files/c57d9562cab4387ad86d32556039631d",1]},{"file":"/snap/nextcloud/28088/htdocs/lib/private/Files/Storage/Wrapper/Wrapper.php","line":603,"function":"releaseLock","class":"OC\\Files\\Storage\\Common","type":"->","args":["__groupfolders/2/Naomi/\u2605Naomi \uc218\uc5c5/Wise/Edu planet/TOEFL Primary MP3/Step 2/step 2 book 3 CD B/30 \ud2b8\ub799 30.mp3",1,{"__class__":"OC\\Lock\\MemcacheLockingProvider"}]},{"file":"/snap/nextcloud/28088/htdocs/lib/private/Files/Storage/Wrapper/Wrapper.php","line":603,"function":"releaseLock","class":"OC\\Files\\Storage\\Wrapper\\Wrapper","type":"->","args":["__groupfolders/2/Naomi/\u2605Naomi \uc218\uc5c5/Wise/Edu planet/TOEFL Primary MP3/Step 2/step 2 book 3 CD B/30 \ud2b8\ub799 30.mp3",1,{"__class__":"OC\\Lock\\MemcacheLockingProvider"}]},{"file":"/snap/nextcloud/28088/htdocs/lib/private/Files/Storage/Wrapper/Jail.php","line":464,"function":"releaseLock","class":"OC\\Files\\Storage\\Wrapper\\Wrapper","type":"->","args":["__groupfolders/2/Naomi/\u2605Naomi \uc218\uc5c5/Wise/Edu planet/TOEFL Primary MP3/Step 2/step 2 book 3 CD B/30 \ud2b8\ub799 30.mp3",1,{"__class__":"OC\\Lock\\MemcacheLockingProvider"}]},{"file":"/snap/nextcloud/28088/htdocs/lib/private/Files/Storage/Wrapper/Wrapper.php","line":603,"function":"releaseLock","class":"OC\\Files\\Storage\\Wrapper\\Jail","type":"->","args":["Naomi/\u2605Naomi \uc218\uc5c5/Wise/Edu planet/TOEFL Primary MP3/Step 2/step 2 book 3 CD B/30 \ud2b8\ub799 30.mp3",1,{"__class__":"OC\\Lock\\MemcacheLockingProvider"}]},{"file":"/snap/nextcloud/28088/htdocs/lib/private/Files/Storage/Wrapper/Wrapper.php","line":603,"function":"releaseLock","class":"OC\\Files\\Storage\\Wrapper\\Wrapper","type":"->","args":["Naomi/\u2605Naomi \uc218\uc5c5/Wise/Edu planet/TOEFL Primary MP3/Step 2/step 2 book 3 CD B/30 \ud2b8\ub799 30.mp3",1,{"__class__":"OC\\Lock\\MemcacheLockingProvider"}]},{"file":"/snap/nextcloud/28088/htdocs/lib/private/Files/Storage/Wrapper/Wrapper.php","line":603,"function":"releaseLock","class":"OC\\Files\\Storage\\Wrapper\\Wrapper","type":"->","args":["Naomi/\u2605Naomi \uc218\uc5c5/Wise/Edu planet/TOEFL Primary MP3/Step 2/step 2 book 3 CD B/30 \ud2b8\ub799 30.mp3",1,{"__class__":"OC\\Lock\\MemcacheLockingProvider"}]},{"file":"/snap/nextcloud/28088/htdocs/lib/private/Files/View.php","line":2050,"function":"releaseLock","class":"OC\\Files\\Storage\\Wrapper\\Wrapper","type":"->","args":["Naomi/\u2605Naomi \uc218\uc5c5/Wise/Edu planet/TOEFL Primary MP3/Step 2/step 2 book 3 CD B/30 \ud2b8\ub799 30.mp3",1,{"__class__":"OC\\Lock\\MemcacheLockingProvider"}]},{"file":"/snap/nextcloud/28088/htdocs/lib/private/Files/View.php","line":2102,"function":"unlockPath","class":"OC\\Files\\View","type":"->","args":["/Documents (shared)/Naomi/\u2605Naomi \uc218\uc5c5/Wise/Edu planet/TOEFL Primary MP3/Step 2/step 2 book 3 CD B/30 \ud2b8\ub799 30.mp3",1,false]},{"file":"/snap/nextcloud/28088/htdocs/lib/private/Files/View.php","line":1202,"function":"unlockFile","class":"OC\\Files\\View","type":"->","args":["/Documents (shared)/Naomi/\u2605Naomi \uc218\uc5c5/Wise/Edu planet/TOEFL Primary MP3/Step 2/step 2 book 3 CD B/30 \ud2b8\ub799 30.mp3",1]},{"function":"OC\\Files\\{closure}","class":"OC\\Files\\View","type":"->","args":["*** sensitive parameters replaced ***"]},{"file":"/snap/nextcloud/28088/htdocs/apps/files_external/3rdparty/icewind/streams/src/CallbackWrapper.php","line":119,"function":"call_user_func","args":[{"__class__":"Closure"}]},{"function":"stream_close","class":"Icewind\\Streams\\CallbackWrapper","type":"->","args":[]},{"file":"/snap/nextcloud/28088/htdocs/3rdparty/sabre/http/lib/Sapi.php","line":136,"function":"fclose","args":[null]},{"file":"/snap/nextcloud/28088/htdocs/3rdparty/sabre/dav/lib/DAV/Server.php","line":490,"function":"sendResponse","class":"Sabre\\HTTP\\Sapi","type":"::","args":[{"__class__":"Sabre\\HTTP\\Response"}]},{"file":"/snap/nextcloud/28088/htdocs/3rdparty/sabre/dav/lib/DAV/Server.php","line":253,"function":"invokeMethod","class":"Sabre\\DAV\\Server","type":"->","args":[{"__class__":"Sabre\\HTTP\\Request"},{"__class__":"Sabre\\HTTP\\Response"}]},{"file":"/snap/nextcloud/28088/htdocs/3rdparty/sabre/dav/lib/DAV/Server.php","line":321,"function":"start","class":"Sabre\\DAV\\Server","type":"->","args":[]},{"file":"/snap/nextcloud/28088/htdocs/apps/dav/lib/Server.php","line":332,"function":"exec","class":"Sabre\\DAV\\Server","type":"->","args":[]},{"file":"/snap/nextcloud/28088/htdocs/apps/dav/appinfo/v2/remote.php","line":35,"function":"exec","class":"OCA\\DAV\\Server","type":"->","args":[]},{"file":"/snap/nextcloud/28088/htdocs/remote.php","line":167,"args":["/snap/nextcloud/28088/htdocs/apps/dav/appinfo/v2/remote.php"],"function":"require_once"}],"File":"/snap/nextcloud/28088/htdocs/lib/private/Memcache/Redis.php","Line":169,"CustomMessage":"--"},"userAgent":"Mozilla/5.0 (Windows) mirall/3.2.2stable-Win64 (build 20210527) (Nextcloud, windows-10.0.19041 ClientArchitecture: x86_64 OsArchitecture: x86_64)","version":"21.0.1.1"}
The trusted domain IP is the servers LAN IP, and it works to connect to it using Nextcloud 20, so that should be correct.
Thank you