Audio dropouts

[simoncn]

This is consistent with a network UPnP discovery issue. Some UPnP servers (I think including Synology) "flood" the network with very frequent device announcements to compensate for other faulty network components that don't handle some UPnP messages correctly. MinimServer uses the ohNet UPnP stack, which doesn't do this flooding and this can cause discovery problems if other network components aren't well behaved.

As you have eliminated most other possibilities, you might need to replace the router to solve this problem.