Connection to MinimServer takes >5 min

[PeterG]

Router is AVM Fritz!Box 7583, as you could see from the configuration attached to each of my posts.
I don't know where to look on it for IGMP snooping and its settings.

Hardly can believe it, but I think I found the reason and solution for the mess.
On my NAS I had a firewall entry for the IGMP protokoll allowed without restrictions and standing first. I replaced it by an entry for UPnP/DLNA and the according MinimServer services (4 in total) and both servers showed up in a second on my T+A, laptop and in MinimWatch.
I'm very sorry for the inconvenience I caused and thank you for the time you invested by looking for a solution.
I've learned new things (IGMP + other) and that leaves it positiv. All this reminds me of a version of "Murphy's Law" for IT-surroundings:
Complex systems tend to complex error behaviour,
simple systems tend to complex error behaviour.