Hello,
I’ve actually been self hosting Nextcloud since late 2016 
… and I’ve never had any issue with my own installations. In the forums I ’ve seen similar issues posted:
(unresolved)
(I hope my issue is also a caching issue - but I do not run the server, so I cannot verify)
I just obtained a more useful log:
25-10-14 17:11:01:028 \[ info gui.scheduler.syncscheduler \]: Sync finished for “/…./Network/owncloud-grafis-epal/” with status OCC::SyncResult::Success
25-10-14 17:11:09:814 \[ info sync.networkjob \]: Created OCC::JsonApiJob(OCC::Account(“user@grafis.sch.gr”), “https://grafis.sch.gr/ocs/v2.php/apps/notifications/api/v1/notifications?format=json”, “GET”, Original-Request-ID: “cac887a9-6f33-42ad-b586-297ed20b9885”, X-Request-ID: “cac887a9-6f33-42ad-b586-297ed20b9885”) for OCC::ServerNotificationHandler(0x5a6f8f0)
25-10-14 17:11:09:815 \[ info sync.networkjob \]: Created OCC::RequestEtagJob(OCC::Account(“user@grafis.sch.gr”), “https://grafis.sch.gr/remote.php/dav/files/user/”, “PROPFIND”, Original-Request-ID: “81c696ef-a182-4148-8fbf-42b68a67dc1d”, X-Request-ID: “81c696ef-a182-4148-8fbf-
42b68a67dc1d”) for OCC::Folder(0x51dc310)
25-10-14 17:11:10:490 \[ info sync.networkjob.propfind \]: LSCOL of QUrl(“https://grafis.sch.gr/remote.php/dav/files/user/”) FINISHED
WITH STATUS “OK”
25-10-14 17:11:59:793 \[ info gui.account.state \]: checkConnectivity blocking: false “user@grafis.sch.gr”
25-10-14 17:11:59:794 \[ info sync.connectionvalidator \]: No system proxy set by OS
25-10-14 17:12:00:593 \[ info sync.checkserverjob \]: status.php returns: QJsonDocument({“edition”:“”,“extendedSupport”:false,“installed”:true
,“maintenance”:false,“needsDbUpgrade”:false,“productname”:“Nextcloud”,“version”:“30.0.7.2”,“versionstring”:“30.0.7”}) QNetworkReply::NoError Reply: QNetworkReplyHttpImpl(0x5a63860)
25-10-14 17:12:00:593 \[ info sync.connectionvalidator \]: \*\* Application: ownCloud found: QUrl(“https://grafis.sch.gr/”) with version “3.0.0.7”
25-10-14 17:12:00:593 \[ info sync.networkjob \]: Created OCC::PropfindJob(OCC::Account(“user@grafis.sch.gr”), “https://grafis.sch.gr/remote.php/webdav/”, “PROPFIND”, Original-Request-ID: “a8c7c252-a1e0-406a-b540-45a615848250”, X-Request-ID: “a8c7c252-a1e0-406a-b540-45a615848250”) for
OCC::ConnectionValidator(0x50f8d40)
25-10-14 17:12:01:537 \[ warning sync.credentials.http \]: Stop request: Authentication failed for “https://grafis.sch.gr/remote.php/webdav/” “a8c7c252-a1e0-406a-b540-45a615848250”
25-10-14 17:12:01:543 \[ info sync.networkjob.propfind \]: LSCOL of QUrl(“https://grafis.sch.gr/remote.php/webdav/”) FINISHED WITH STATUS “AuthenticationRequiredError, Host requires authentication”
25-10-14 17:12:01:543 \[ warning sync.connectionvalidator \]: \*\*\*\*\*\*\*\* Password is wrong! QNetworkReply::AuthenticationRequiredError OCC::PropfindJob(OCC::Account(“user@grafis.sch.gr”), “https://grafis.sch.gr/remote.php/webdav/”, “PROPFIND”, Original-Request-ID: “a8c7c252-a1e0-406a-b540-45a615848250”, X-Request-ID: “a8c7c252-a1e0-406a-b540-45a615848250”, NetworkError: “Host requires authentication”)
25-10-14 17:12:01:543 \[ info gui.account.state \]: AccountState connection status change: OCC::ConnectionValidator::Connected → OCC::ConnectionValidator::CredentialsWrong
25-10-14 17:12:01:543 \[ info gui.account.state \]: Invalid credentials for “https://grafis.sch.gr/”
25-10-14 17:12:01:543 \[ warning sync.credentials.http \]: Invalidating the credentials
25-10-14 17:12:01:543 \[ info sync.account \]: Clearing cookies
So at 17:11:01:028 a sync finishes successfully and after one minute that the client tries to reconnect but gets a Password is wrong!
As for the last part:
Please explain this in more details - does it mean users who hit the problem setup accounts in a different way?
the service provides accounts to all students, teachers and schools of Greece. There is no difference in the setup of these accounts. The Nextcloud instance doesn’t know if a user is a teacher or a school unit. I have a teacher account that works fine. The account of my school has the problem. The only difference I can think of is that I am not really using my personal account (I use a self-hosted nextcloud server) whereas the school account is much more active.