Can not see minimserver on Android or google tablet via wifi

[jcswlondon]

I've been running Minimserver okay for several years.
Swapped home router from an Asus to Draytek and now neither Android phone nor Google Nexus tablet can see Minimserver.

Minimserver on Windows 10 Pro 64bit
Java 8 Update 241
Minimserver 2.2 update 240
Wifi 2.4Ghz with 5Ghz switched off
Firewall on router switched off

Foobar2000 on a different Windows 10 PC on either wifi or wired can see Minimserver.
Google tablet on wifi can see BubbleUPnP on Android phone but can not see Minimserver.

Android phone can see
http://.......:9790/ my Minimserver configuration webpage

Android phone can see
MusicBee DLNA from same PC running Minimserver

Android phone does not see Minimserver
I test this both with what BubbleUPnP can see and a UPnP Explorer app.

If I plug back in Asus router it all works okay again.

Draytek support suggested enabling WAN UPnP on the router which I have tried. It does not help, should not help and is an unwanted setting. Draytek documentation says it is only necessary to enable UPnP if you want it via WAN.

I have experimented with opening ports 9790-9791 and 1125-1126 in router NAT for local IP addresses but that has not helped.

I considered trying different ports to 9790 and 9791 but those settings are greyed out in Minimserver.

Currently stuck for any other ideas to try.