Thank you for the reply, but having regular 1-second stalls is still highly irregular - the delays are too large IMO to be considered a regular frame pacing issue. Do you have any hypotheses regarding why it might be happening? Are there any requirements to where drawableSize must be updated to avoid these stalls?

Changing drawableSize also seems to somehow disable VSync (or whatever it's called on MacOS). For a very lightweight application, the time it takes for nextDrawable to return goes from ~6-7ms (120fps) to almost zero.