Update from 19.0.4 to 19.0.7 failes

I tried to Update from webinterface, but get “backup failed”. No error-info. I looked for info in /var/log and with occ log:tail oder occ log:watch, but there is nothing.

Where do I get info about that failure?

OS is Debian for Odroid on XU4, NextCloudPi version v1.34.1, PHP is 7.3

Space for backup: 390GB, /(root) has 7GB free, /tmp is 1% full.


Found it:
Logfile goes to files-folder and not to /var/log …

Error was:
not readable/writable. Reason: the file was owned by root. The last bunch of updates did not fail because of this file (it left from installation).