Mp4 exports are exporting as incomplete files.
Generally, the sound will be playing and the playhead will be moving but the visual will be stuck on a single frame.
This happens at the beginning of exports and also at the end sometimes.
This has been an issue since Premiere 2021 & 2022 across MAC Intels (iMacs) and M1s.
My current scenario:

Premiere 23.1.0
Here's the exported video link, you'll see the problem.
https://vimeo.com/802867731/38f9e8a223
What isn't apparent in this export is that the OUT point is like 5 seconds longer then what was exported. So it literally just got the OUT point wrong in this particular example.
Pretty infuriating that this has been happening for years and has been a pain in my company's workflow for quite some time.