Playback monitor unwanted switch and interface slowing down

1. Often when I open Premiere Pro the designated monitor for full-screen playback (*) has switched from #2 to #3. Come to think of it, it might only happen after a computer shutdown. (If I shut down Premiere and restart without shutting down the computer it is usually still set to the right monitor).

(*) Settings > Playback > Transmit Device Playback

I'm on a Mac Studio Ultra (Ventura 13.4), three monitors. The main monitor (#1) and my preferred Playback monitor (#2) are connected via Thunderbolt, the other monitor (#3) via the HDMI output. Is that the issue maybe? That Premiere Pro assumes that the HDMI output most likely is the Playback monitor?

Anyway, it's not a big deal but still annoying that I have to switch so often before I can get to work. Maybe I'm missing something? Tips are welcome.

2. I'm still having issues with the interface slowing donw after a couple of hours, forcing me to quit Premiere and restart. After the restart initially everything works okay until after a few hours everything starts to slow down again. Playback is not affected, but everything else gets slower and slower until it's unworkable.

It kind of feels like a memory issue. Like some memory is filling up over time and it having to cope with more and more data.