You can also try generic searches from some of the errors you are seeing like “save login to session”. Perhaps something can be found there:
https://help.nextcloud.com/search?q=save%20login%20to%20session
Try searching a bit more. If nothing turns up you’ll probably want to file an issue and share logs with the developer / maintainer, plus link them to this topic.
You can also link the github issue your create back here.
Sounds frustrating.