So I have a timeline with 1440by1080 23.98 Xh-A1 footage. My second camera was the HV20. I exported the HV20 footage to compressor to transcode to ProRes22 and changed it to 24 fps and selected reverse telecine.

(I did this since the HV20 footage is captured at 29.97 interlaced by FCP, and since it needs to be 24 fps and progressive to edit on the same timeline with progressive footage from the Xh-
A1)

When I put them on the timeline together, the audio from the HV20 goes off track like 10 minutes after the sequence starts. Is this because the Xh-A1 is 23.98 and the HV20 is 24 fps? Do I need to "write-in" 23.976 in the ProRes settings in Compressor when transcoding?

So it's fixed. Having one camera with 23.976 and one with 24 throws off the audio eventually. In compressor, choosing 23.976 for the HV20 footage was crucial if the other cams footage is 23.976. 24 is no good.