Thanks for your reaction, I’m still not be able to fix my problem.
I followed https://www.virtualmin.com/documentation/web/troubleshooting and everything seems correct. No *, but real IP addresses for all sites-enabled configs. All error_logs are empty.
I cloned a correctly working virtual server in the hope this would solve things, but it resulted in the same problem. So it’s still randomly showing the default website or the correct website of the new domain. If the correct website is showing, half of the assets are nog loaded (because of ‘net::ERR_ABORTED 404 (Not Found)’ errors). Does this give any clues?
Compared to the previous virtual hosts that were set up without problems, the only difference I can think of is that an SSL certificate was installed for one of the domains in the meantime. I do also notice that the new domain, https://xxx.net, redirects to this SSL-enabled domain, even though this does not happen for the existing virtual servers.
I would be very grateful if you have other ideas to solve my problem.
Edit: also, when I change the domain name of a correctly working virtual server to my new domain name, this results in the same random problems. When I change it back to its original domain name, that domain works perfectly again…