Nextcloud app 3.0.0 cannot login to nextcloud server 11.0.5.1

Unfortunately you updated the app to version 3.0.0 and shot all connections to (at least) nextcloud 11. According to logfile the login works:

{“reqId”:“SUml+GU6JIY2QoKjugq3”,“remoteAddr”:“188.193.244.YY”,“app”:“admin_audit”,“message”:“Login successful: "frank@ithnet.com”",“level”:1,“time”:“2018-02-11T14:02:38+00:00”,“method”:“POST”,“url”:"/ocs/v2.php/apps/notifications/api/v2/push?format=json&pushTokenHash=9646568dc2c20505b98b317bf3956c76a4d632c1eaa52b4ace3c0959fa40a0758cc6663f6137d39eae090bf8a72ef4e2d5fedf8e8e181092bf3410c78d461c14&devicePublicKey=-----BEGIN%20PUBLIC%20KEY-----%0AMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAiO8R5ovEN6zHs8%2F5phEr%0AwFj%2B03Gq%2BfKR6Yq4V3qNdqxuc%2F5yBClsejTJOaoCxAUbkM5VpitznRSFjwQESHvP%0ArxL3OISZepRBAJZLDq3FWV24WGLcXQFZPoN3m%2BqYIScQK6Q4IYGB%2F3bIvABhiav4%0A2fffGcSyywuiROPn4pjECZd6PPQ8PAqE%2Fl5jZpvibM9JuPGcbe%2F%2Bm1H8TVXAWTUh%0ALfOt8BKI2LdJeaBU9k4MmDtZZ3JCk78nYgV6C3Xw4mSM58C9b8aX6I1xPCJErbsK%0AipA7OG7ixCMAB%2F2pN1FGQzSEC1PSyEb3RSRFKT8VfJJWmBSkzjTFInDR0tA0HKwC%0AGwIDAQAB%0A-----END%20PUBLIC%20KEY-----%0A&proxyServer=https%3A%2F%2Fpush-notifications.nextcloud.com",“user”:"frank@ithnet.com",“version”:“11.0.5.1”}

But then:

{“reqId”:“sghjUlD/8F/aFr1yqZA6”,“remoteAddr”:“188.193.244.YY”,“app”:“webdav”,“message”:“Exception: {“Message”:“HTTP\/1.1 401 CSRF check not passed.”,“Exception”:“Sabre\\DAV\\Exception\\NotAuthenticated”,“Code”:0,“Trace”:”#0 \/srv\/user-local\/cloud.default\/owncloud\/apps\/dav\/lib\/Connector\/Sabre\/Auth.php(154): OCA\\DAV\\Connector\\Sabre\\Auth->auth(Object(Sabre\\HTTP\\Request), Object(Sabre\\HTTP\\Response))\n#1 \/srv\/user-local\/cloud.default\/owncloud\/3rdparty\/sabre\/dav\/lib\/DAV\/Auth\/Plugin.php(199): OCA\\DAV\\Connector\\Sabre\\Auth->check(Object(Sabre\\HTTP\\Request), Object(Sabre\\HTTP\\Response))\n#2 \/srv\/user-local\/cloud.default\/owncloud\/3rdparty\/sabre\/dav\/lib\/DAV\/Auth\/Plugin.php(150): Sabre\\DAV\\Auth\\Plugin->check(Object(Sabre\\HTTP\\Request), Object(Sabre\\HTTP\\Response))\n#3 [internal function]: Sabre\\DAV\\Auth\\Plugin->beforeMethod(Object(Sabre\\HTTP\\Request), Object(Sabre\\HTTP\\Response))\n#4 \/srv\/user-local\/cloud.default\/owncloud\/3rdparty\/sabre\/event\/lib\/EventEmitterTrait.php(105): call_user_func_array(Array, Array)\n#5 \/srv\/user-local\/cloud.default\/owncloud\/3rdparty\/sabre\/dav\/lib\/DAV\/Server.php(466): Sabre\\Event\\EventEmitter->emit(‘beforeMethod’, Array)\n#6 \/srv\/user-local\/cloud.default\/owncloud\/3rdparty\/sabre\/dav\/lib\/DAV\/Server.php(254): Sabre\\DAV\\Server->invokeMethod(Object(Sabre\\HTTP\\Request), Object(Sabre\\HTTP\\Response))\n#7 \/srv\/user-local\/cloud.default\/owncloud\/apps\/dav\/appinfo\/v1\/webdav.php(61): Sabre\\DAV\\Server->exec()\n#8 \/srv\/user-local\/cloud.default\/owncloud\/remote.php(165): require_once(’\/srv\/user-local…’)\n#9 {main}",“File”:"\/srv\/user-local\/cloud.default\/owncloud\/apps\/dav\/lib\/Connector\/Sabre\/Auth.php",“Line”:220,“User”:“frank@ithnet.com”}",“level”:0,“time”:“2018-02-11T14:02:57+00:00”,“method”:“PROPFIND”,“url”:"/remote.php/webdav/",“user”:“frank@ithnet.com”,“version”:“11.0.5.1”}

All from the same IP with the same account, 20 seconds later failed.
Why is that?

@tobiasKaminsky @Andy

Cross-posted it to the issue tracking and login issue: https://github.com/nextcloud/android/issues/2133#issuecomment-364993747