Allen&Heath SQ MixPad application does not stay connected to remote mixer

[STEPHANVS]

We have an Allen&Heath SQ5 mixer, which is connected to the LAN. Mixer can be accessed via its app, SQ MixPad.

If I connect to the OpenVPN server running on a Synology NAS and try to connect to the mixer remotely (NAS and mixer are on the same LAN), then initial connection works, but then no update is received and the app disconnects.

What I found out is the following:
In terms of ports: Discovery: 51320 <- most probably used to discover the Mixer on the LAN
Server-side: 51326 <- most probably the port on which the mixer is listening
UDP Port Numbers start: 51324 <- not sure about these

Unfortunately, running the app remotely is not supported, which I understand, however it should be possible. I tried both the Windows and the Android app, both behave the same way.

Does anyone have any idea what should I try?