The server is once again online and will remain that way for some time to come.

I had to switch DNS records from my home-router to my Public-ip-relay while doing that I noticed that I'd given the murmur.hendrikpeter.net sub-domain a whopping 1 day of DNS cache (meaning that it will take up to a day for murmur.hendrikpeter.net to point to the actual Nuc running the new mumble server).

So if you really want to connect in the next 24 hours you can do so via: murmur-temp.hendrikpeter.net with otherwise the same credentials; ports and settings as described near the bottom of OP.