FCPx - 4k Video with audio clip and digital audio clip - audio drift

Hi,

Longtime FCP user but still relatively newb with some of these issues as I only dabble.

I have a video clip from a Canon 4k camera which includes audio, and an audio clip from a mixing desk.

My issue is that when I try to align the 2 clips in FCPx, the audio from the desk clip gradually drifts from the video.

I have used markers at the beginning and the end of the 2 clips and used the clip retime feature in FCPx to retime the clip so both markers align. Playing the clip around the markers, audio sync is fine. If I click anywhere in the middle of the timeline (the clips are an hour and a bit in length), the 2 clips are out of sync by about 1-2 seconds. The 2 clips are obviously from different sources and I've tried retiming either clip, using the audio as the first clip in the project, using the video as the first clip, and setting the project defaults before dragging the clips.

I have access to Compressor and used the Apple ProRes 422 template to rework both clips, but I get the same result.

I've read plenty about this but am really stumped as applying those other solutions to my problem does not seem to change the result. I cannot understand how using 2 pairs of aligned markers at each end of the retimed clips does not result in the interim portion of the clips aligning.

I'm currently running the clips through Compressor with a copy of the Apple ProRes 422 template but with forced changes to the audio bit depth and the video frame rate of both clips.

Here's hoping I've chosen the right settings, screenshots from the Compressor job are also below.

My questions are, is this the right approach and have I chosen the correct settings in Compressor? Do I need to force a render of both clips after the retime? (Which I did try, to no success).

Screenshots below from FCP, MediaInfo and Compressor on the 2 clips.

Cheers

Tim

Mac Studio, 32GB, Ventura 13.4, FCP 10.66, Compressor 4.6.4