NCP: CalDAV and CardDAV broken (automatically, last few days)

I did have a fully working installation and just realized that the contacts and calendar are not syncing.
Then I saw that the web-interface shows an empty (!) calendar and no (!) contacts.

The Admin user was able to display this here:

Ihr Webserver ist noch nicht hinreichend für Datei-Synchronisierung konfiguriert. Die WebDAV-Schnittstelle ist vermutlich defekt.

Ihr Webserver ist nicht richtig konfiguriert um "/.well-known/caldav" aufzulösen. Weitere Informationen hierzu finden Sie in unserer Dokumentation ?.
Ihr Webserver ist nicht richtig konfiguriert um "/.well-known/carddav" aufzulösen. Weitere Informationen hierzu finden Sie in unserer Dokumentation ?.

This issue appeared in a timeframe when I did not change any config. I assume some autoupdated changes caused it.

Since I have no idea how to fix this I chose to wipe it clean, reinstall and then try restore my backup.

Fun part: Reinstallation fails (I’ll open a second topic)

Something is really wrong with some recent update.

Please provide more information about the way you installed your instance, what else did you install and on what device.
If you use ncp please provide as well the ncp-report.
Thanks

This topic here is mainly for information since I did wipe the installation and can not provide more reports.
It happended on a Raspberry Pi 3b, Raspbian 32bit OS (fully updated). NCP was installed using the curl installscript.

To be more helpful in future cases: Can you explain what you mean by “the ncp-report”? I am a nontechnical noob so I do not know.

Ok. I think we got further in your case.
First of all. Nextcloud dropped the support of 32-bit.
So it is most likely possible to install ncp and Nextcloud on 32-bit systems but there are many apps which will not work or have an unexpected behavior.
Most important is, that you are on uncharted terrain and it will be almost not possible to give you support.

The ncp-report is a command. Which can be used in your terminal (on the monitor or via ssh) and it shows all important log files and data at once.
The report can easily be copied into a forum post.

Ok, thanks for clarifying the ncp-report thing. I can run that in terminal next time.

With regards to the OS I totally did not know that a 64bit version was a requirement. I did use the official raspberry Pi Imager v1.7.3 and thought it is best to stick with the recommendation (which is “Raspberry Pi OS (32-bit)”).
Under “other” the imager offers: “Raspberry Pi OS (64-bit)”
So I understand that I should use this one then, right?

Yes and it is totally able to handle 64-bit.
See: Raspberry Pi OS (64-bit) - Raspberry Pi

@Gorf While I second the recommendation to use 64bit, I do not think that this causes your particular issue.
Can you please execute the command

sudo bash -c 'source /usr/local/etc/library.sh; clear_opcache; systemctl restart php*-fpm

and see if it solves your issue?