Issues with VLAN traffic for TV

[fossxplorer]

I am using OPNSense behind a fibre router box (from AltiBox Norway) and things work fine except for the TV. One of the OPNSense  LAN ports are connected to the TV box from the ISP and when watching TV channels it would work for a couple of minutes and then turn black. What helps is to change the channel, then it would work for another couple of minutes.

The router is used in the standard (non bridge) config and it will deliver TV on VLAN 101 and internett on VLAN 102. So both VLANS should arrive at WAN port of OPNSense, which is set as the DMZ IP in the router config.

I have messed around with the VLAN setup to no help.

Any help will be appreciated!

TIA!