Intermittent frame rate drop on M1 Mac

I run Zwift on an M1 Mac mini running Sonoma.

This used to work perfectly, but over the last couple of months there has been an intermittent glitch where the frame rate drops noticeably and does not recover until you restart the program. Mostly this seems to drop to a few Hz - looks like fewer than five fps, so you get very jerky motion, but this morning it dropped catastrophically - I was getting perhaps one frame every five seconds, and that wasn’t being rendered properly - so in some you only saw bikes and not riders.

I checked Activity Monitor on the Mac and it claimed that Zwift was using over 200% CPU - nothing else was using abnormal amounts of system resource.

This morning, the slowdown definitely happened when I got the burst of confetti for a sprint PR, and thinking back, I am pretty sure that the other slowdowns I have seen were also triggered at the end of sprints.

Has anyone else seen this? I lost 7 miles of a ride this morning as I had to completely restart Zwift, which was not good, and I then spent the rest of the ride deliberately slowing down on sprints so as to avoid triggering the confetti…

Haven’t seen this recently – nor ever in that extreme, but you might want to look at I/O. If you have a storage device that is failing or is trying to mount (like a Time Machine backup disk waiting for a password to unlock it) you can see this sort of behavior.
The build tin disk utility program might have a warning about some imminent failure. YMMV