HLS Manifest Error

Hello, I need a bit guidance here with HLS stuff :(...I moved to a new flat and got a new internet connection with IPTV over HLS. The problem is, they gave me a crappy Huawei optical modem with it which I dont want to use as a router. So I wired it to my Asus, everything but the HLS streaming from the IPTV provider works fine. Streaming works when I connect a device directly to the modem, but not when I connect to the OpenWRT router.

Their site says that Im connected from their ISP partner, so I suspect that there is something in their infrastructure that messes up the HLS. I can watch the stream while connected to OpenWRT only while using VPN.

Any idea how to set this up properly? I dont even have admin account for that Chinese ****.