Thanks for the suggestions, Andrew.
The DLNA receivers - my Sonos speakers - are available for a while after re-start or 'refresh zones', then disappear.
- The options 'firewall' and 'subnet' shouldn't be the cause then?
- i don't know what 'forwarding multicasts' means. Will need google that
- 'changing addresses': I have not seen this happening, addresses seem to stay the same
Overall, i am puzzled because this worked with the same setup for the longest time, as in years. Not sure if I changed any settings, but would not have any idea which that would be. Also not sure if that started with a MS W10 update on my ComputeStick.
Either way, it's unfortunate, because I can't use JRemote anymore where i used it most - at home. I started using Spotify to play to Sonos, which has some advantages anyways, of course, but i'd still prefer playing from my own library and with my own play menus via JRemote.