Can't Export Quicktime - Error compiling movie

I am in a real pickle here. I shot some simple video on an FX3 in XML. I imported fine, it plays fine in Premier Pro. I sync'd it with audio into a multi-frame sequence and through on a standard rec709 LUT. It WILL NOT export as a quicktime. I have tried a bunch of suggested tweaks - I removed the LUT, I simplified the sequence, I tried changing the Preview settings, I have tried exporting using both hardware and software, I have rebooted, I have upgraded Premier, I have reinstalled Ventura, I tried tweaking most export settings.  A couple other things to note:

- I can export the individual clips straight from the bin.

- I can export as H264 but when I try to open it with Quicktime, I get the "This file contains some media which isn't compatible with Quicktime Player." (probably a separate issue)

- I have other sequences in the project that will export as QT but those we created with different imported media (from an iPhone).

- I can export QT sequences from another project that features, FX6, 9 and GoPro footage.

So I'm at a loss. Any suggestions?