I just migrated from NC 13.0.12 to 14.0.8 to 18.104.22.168 on debian jessie with Apache 2.4 and PHP 7.3. All fine so far for two other instances where I did the same steps as described below.
In my last instance, I encountered a warning when enabling the twofactor_* apps: “enabling this leads to instability” or similar (in yellow). However, that was AFTER I was installing an app through the app store within the web interface. I think it was after I installed twofactor_admin (not sure, though). After that, the server was inaccessible through web.
It gets accessible as soon as I manually delete the apps/twofactor_u2f folder via shell and it gets inaccessible (internal server error) as soon as I install twofactor_u2f, no matter whether other twofactor_* apps are installed or not.
I see the errors in NC log below but have no clue what they mean: https://seyfarth.de/nextcloud/u2f-errorlog.txt (170kB, please cite relevant parts, file will be deleted once not needed nay longer). Any hint/help/ideas what to try?