I see this often on Apple TV, and I think on iOS as well.
I’m watching a live event “away from home” (server in another location) and slowly the picture becomes blockier and blockier. Happens over the course of 20-30 min I think. It’s not stuttering or dropping frame, just really low quality. If I exit to the guide and then restart the same stream, it comes back at normal high quality.
These are all streams through fox or nfl+. Maybe it’s an eplus issue or a fox issue. Anyone else see this?