[closed] Problem with NextcloudPI (unsuccesfull?) upgrade to 13.0.3

A few weeks ago, I could start an upgrade of my NextCloudPI to 13.0.3. But after that upgrade, there were problems. I cannot figure out when or how, but after some usage, I get a 503 Service Unavailable. I even cannot ssh into my RaspberryPI.

After reboot, I get, every time a page that I have to upgrade to 13.0.3.
Before upgrade I have this relevant system info:
|NextCloudPi version|v0.56.17|
|NextCloudPi image|NextCloudPi_12-04-17|
|distribution|Raspbian GNU/Linux 9 \n \l|
|Nextcloud check|ok|
|Nextcloud version||

And Nextcloud configuration:
updater.release.channel stable

The difference in version is strange…

After the upgrade to 13.0.3, I have same system info as above, but the Nextcloud configuration says the version is All seems well now, but after a while (after some usage), I get a 503 again.

How can I analyse this further?

Previous upgrades (even from 12 to 13) went without issues…

[EDIT]: I did a complete re-installation.