Nextcloud removes custom group memberships on login
If you create a custom group of users in Nextcloud and add a Stackspin user to it, then when that user next logs in to Nextcloud via Stackspin OIDC, that membership is revoked. Apparently the social_login app resets the list of groups to only the ones we specify in Stackspin. This is rather nasty, and also strange because the app specifically prepends the name of all groups it creates with a prefix so they stay separate from groups that are created in another way.
I'm hoping this will be fixed by switching to another OIDC app for Nextcloud: nextcloud#1077 (closed)