no playback and random error messages

[DesertPigeon]

So I bought a new Interface at the start of the year, the Steinberg (Yamaha) UR-RT4 and it has worked magnificently.
So magnificently in fact I was using it just last week to record, mix and master a full processing-heavy session.

I load it up after trouble loading another session today and there's no playback, I'm met with a seemingly random rotation of these two error messages:
-AAE 6009 (to which I tried all of Avid's troubleshooting methods, to no avail)
-Pro Tools ran out of CPU power. Try de-activating or removing Native plug-ins. (AAE error -9173)

This second one makes the least sense, my CPU is a Ryzen 9 3900X and even if I deactivate every plugin I still get this from the first time I press play from startup.

I have updated the drivers for everything, I even un-and-reinstalled pro tools, the odd time I actually got some playback on the one session, to only then have another one of these messages randomly thrown at me on the one I wanted to open. I get playback on a session that has one midi synth so evidently, it's possible.

I tried committing the tracks with intensive plugins, pro tools just closes, sometimes I don't even get an error message, it just stops responding, it's driving me mad and it's worse knowing that my setup has been running fine before today.

[junkgear]

Has anything changed on your system outside of Pro Tools? Any new software installed or anything that may also use the UR interface for audio?
Is the Windows task manager showing excessive CPU usage when these errors happen and if so, what processes is using the most?

Have you tried holding N down when PT starts, then re-selecting the UR as your audio device. Maybe also try increasing the buffer size to see if it helps.

Are you loading your sessions from the same drive as you always do? Just looking for something in your workflow/setup that may have changed.