Even without any change, Apache does "not restart after the configuration change for website"

My ISPConfig installation is in a state in which any website change, even if no actual changes are made, results in log entries like "Apache did not restart after the configuration change for website" and "Saved non-working config as /etc/apache2/sites-available/website.err". No ".err" file is there, though. Neither "systemctl status apache2.service" nor "journalctl -xe" produce any information about what happened, and /var/apache2/error.log or the website's error.log don't help, either...

Any idea what may have gone wrong, or where else to look?

Cheers,
Etc

 

It happens with every website I touch, regardless of what I change in it.
It's impossible that all my website configs would be bad. Everything works perfectly except from this issue.
When the messages show up in the ISPConfig log, they obviously show the site I last touched.
it seems that my changes actually were made and written into the .vhost file.
And even though ISPConfig says it saved the bad configuration in an .err file, it doesn't actually do that. There are no .err files. (Sorry, can't show the actual directory listing.)

apachectl -t doesn't help, as there is no error in Apache; there wouldn't be even after an .err file would have been written. I would have to manually reinstate the bad file to do that, but as I said, there is no such file.

 

Of course ;-)