Proxies not playing back well and freezing in multicam, raw playing back better

We’re cutting a documentary that was shot with three+ iPhone cameras (13Pro, 15Pro, 15ProMAX, 16Pro, 16ProMAX, and 17Pro) as well as two image360 cameras. Some of the clips are 2+ hours long. We made ProRes Proxy proxies and made multicam sequences (some over 18 hours long) with four+ video tracks.

Some of our iPhone clips are causing the multicams to stutter then freeze. We think it’s because the iPhones shot variable frame rate, which is somehow causing an issue with the proxies. (Is ProRes Proxy constant frame rate? or can it also be variable frame rate?)

ChatGPT is telling us that to transcode the iPhone footage to ProRes LT. Would that help?

Bunch of questions below because ChatGPT lies sometimes:

Is ProRes LT always constant frame rate? Or can it also be variable frame rate?

Can ProRes LT be attached to source clips as proxies? 

Is ProRes LT 10-bit? (The iPhone footage appears to be 10-bit HEVC.) If so, would an optional workflow be to replace the iPhone footage with ProRes LT transcodes and not link back to the iPhone footage before turning over to color? Or is there a way to relink the source clips to LT, cut with LT, then relink back to the iPhone footage without audio drift issues (since some clips are 2+ hours long).