Hello everyone, including the pro's!
I've done quite some search here to try to solve this alone, but it seems that the standard solutions do not bring me any further: I would really appreciate some specific help.
I created subdomains MU install (not folders). I set the main domain to wildcard subdomain forwarding, but also created rules for subdomains to be forwarded to the root folder of their main domain name. They do work on the multisite, *except* one - and that's the problem.
The single not-working subdomain does not work, with or without forwarding rule or wildcard.
History: For an upgrade, my provider "forced" me to change servers. I did this manually, database, install files, etc. Maybe I missed something? I love this site - can I save it?
I even believe that mechanical forwarding works, since it works with the equal-configured sister-subdomains, but some kind of malconfiguration of my wordpress installation (?) does just not accept this one subdomain.
My excuses in case this error is derived from a lack of nerve cells and thanks a lot for putting your powers to work!