Every time you switch to another stream, it selects the highest quality that isn’t higher than what you were watching last time. One moment you’re watching 1440p60 9 Mbps HEVC, completely stably with low latency. Next you hop into a 720p30 stream. Fine, the source is what it is. Then you open a 1080p60 stream. You get 480p30 because 1080p60 and 720p60 are both more than 720p30. Completely uncalled for when your actual selection was 1440p60.

Auto quality is no solution. Its bandwidth estimation keeps having downward spikes. It may say 135 Mbps which is still an underestimate but plenty. Suddenly it jumps to 4 Mbps, 2 Mbps, 700 kbps, apparently driven to decrease further every time it selects a lower quality. It will often bottom out at 360p30 or whatever the minimum is. It may stay there for a few seconds or a minute before instantly jumping back up to 88 or 200 Mbps, repeating the cycle. There’s never an actual hitch, just constantly cycling quality. Manual source quality runs fine.

macOS Tahoe Safari and Firefox seem more susceptible to the auto quality issue than Windows 10 Firefox. Windows has spikes but doesn’t drop as low as often. 18 Mbps, whatever, still enough. It does still drop lower at times. I saw 160p30 just now. The first issue of manual quality ratcheting down is universal, affecting everything identically.

Up to a few months ago I didn’t have issues with this. You’d generally stay on source, certainly never 480p30 or lower for no reason. It’s driving me nuts that I keep having to select source quality manually.