For some reason, Pico-8 seems to be slowing down to 30fps about every second or so and then going back to 60 a short while after, even in a practically empty cart. Here's a simple cart to show what I mean, although the ctrl+p CPU display shows it much clearer, it doesn't seem to show up in gifs, and I have no other way of recording it.

All this cart does is add 1 to a variable every frame _update60() is called, and clears that variable every frame _draw() is called. If Pico-8 is running at full speed, it should always be 1, which it is on the BBS's html player, at least for me. On my computer (Windows 10 1903), this cart does this:

It's also seemingly caused some problems with sound effects, as it seems like whenever a sound effect is played during one of these stutters it doesn't come out until it's done, but I'm not sure.

It's definitely a lot less than once a second for me, but I am seeing occasional blips running the cartridge on 0.2.1b.

Interestingly, I'm also seeing the lower line in the ctrl+p display ramping up and dropping back down for no visible reason. I wonder if the blips happen at the top of that ramp?

That said, the version running on web on the forum is showing neither behavior. Possibly a bug that was fixed?