Let's Encrypt certificate for main hostname not working

Hi. I have a server with a hostname “host01.domain.tld”, just testing it.

I created first the virtual server “host01.domain.tld” (exactly as the hostname), as the first domain on server (no other virtual server defined, ever).

I requested a Let’s Encrypt certificate, everything went smooth. But it’s not working for https://host01.domain.tld/index.php (a test PHP file), I still get the old self-signed certificate.

I copied it to Webmin and Usermin. There it is working ok!

I created a new Top-Level Server, “test01.domain.tld”, to see what happens. Did exactly the same thing, and there it is working ok! Https links work ok from the start after requesting a Let’s Encrypt certificate.

I restarted apache, renew the certificate, but I still get the old self-signed one for “host01…”.

Server has CentOS 7, latest updates to Virtualmin GPL etc. - “yum check-update” shows there is no update.

Any ideas what could be wrong?