Hi @arne_f,
It isn’t a single service - Multiple others have said they have issues with Discord as well after Core 153. At least one user (@prussbw) has downgraded back to Core 152 and they have confirmed Discord functionality was restored.
Another user (@metallhase) cannot connect to CS:GO anymore after updating from Core 152 to Core 153. Post: Update 152->153:Gameserver not reachable
My understanding is that all three services utilize WebRTC and so WebRTC seems like the common element here.