control point has problem finding MinimServer

[RuudS]

The problem I have is that the control point I use doesn’t detect MinimServer. After a long while it does and all works fine (playing music to my Dune media player). Most of the time things continue to work. I think that’s because I regularly select other music or other ‘orders’. When music plays for some time on its own, the control point doesn’t find MinimServer when I try.
I read some tips on the internet and tried some things without the wanted effect.

My setup:
MinimServer is running on Synology DS214play
DSM 6.2.4-25556 Update 5
The Synology is connected by wire to my router.
Normally there is an ASUS RT-AX58U as an access point in between, but without that the problem is still there.
Router: Ziggo modem = Compal Connectbox v1.
As control point I use the app ‘Na Remote for Dune HD Pro’ (on some mobile phones and on a tablet). The mobile phones sometimes use the wifi on the AP, but using the wifi from the router doesn’t make it work.

I tried completely disabling the firewall on the Synology. Control point (mobile phone/tablet) and the Synology DS214play are on the same subnet. My conclusion is that the problem can be the issue with multicast you mention on the troubleshooting page.
I cannot find an IGMP snooping setting on the Synology DS214play.

I hope you can help me solving this for my setup.