Desktop client crash - how to recover?

Since recently I have problems with my Nextcloud 3.1.3 app on Windows 10 Edition 2004 (all security updates installed). The app simply crashes and disappears (app windows close, systray icon disappear as soon as I hover it with my mouse) - typical signs for an app crash.

App is configured to sync to three Nextcloud servers (two productive (23 GB and 189 GB, one development (0 GB)).

If I’m fast enough I can pause sync and thus app keeps running - but if I start sync on one of my productive accounts (no matter which one, both have changes), I can watch the sync start and then after some time the app disappears.

I tried starting nextcloud.exe with –logwindow parameter, I can see the log, but it doesn’t help as the window disappears as the app crashes. Even though I checked permanently save logs I can’t find a file this log gets saved to - where is it?

Files in %appdata%/Nextcloud/*_sync.log only inform me about started sync, nothing more:

#=#=#=# Syncrun started 2021-03-14T10:14:53Z
#=#=#=# Syncrun started 2021-03-14T10:16:05Z
#=#=#=# Syncrun started 2021-03-14T10:16:38Z
#=#=#=# Syncrun started 2021-03-14T10:17:59Z
#=#=#=# Syncrun started 2021-03-14T10:18:51Z
#=#=#=# Syncrun started 2021-03-14T10:19:50Z
#=#=#=# Syncrun started 2021-03-14T10:20:24Z
#=#=#=# Syncrun started 2021-03-14T10:21:07Z
#=#=#=# Syncrun started 2021-03-14T10:22:44Z
#=#=#=# Syncrun started 2021-03-14T10:27:02Z
#=#=#=# Syncrun started 2021-03-14T10:30:54Z

Nextcloud client on my notebook (same configuration, only two productive accounts and way less files synced) currently works without problems.

Where to continue looking for errors? How to recover?
Ideally without having to download 200 GB again, this takes some time…

Thanks in advance.

PS: To recover I tried installing Nextcloud 3.2.0-rc1, but it says that all servers are incompatible and I can only continue on my own responsibility, so I downgraded back to 3.1.3

No ideas how to proceed?

I think maybe some internal database or such could be corrupted - I had some blue screens before because of that shitty Windows Update that disabled some printers.

My recommendation would be to reinstall the Nextcloud desktop client…

Not sure my issue is the same or not. (sounds very similar) I use client on 2 pc’s (both win10) one at home, working fine, and other is Office. (where i actually need it) is not working. (also on 2 phones)
-office - I manually launch it, can see it pop into the task manager (on 2 or 3 of the tabs) but it instantly clears out. nothing pops up.
I was thinking a change in the default (windefender(off!) or winsecurity, but i have found nothing. was there a KB update for win that now blocks it, that hasnt hit my home pc ?? ive uninstalled and reinstalled the latest nc, but no change.