Weird extra process and unreadable output!

Dear Sirs: What the heck is going on??! Been rendering for the last 17 hours, upscaling to 4K (Proteus). When the process was seemingly finished, VEAI3 started some random process afterwards, which I aborted (as it would take an extra hour):

The real movie was:

And the latter comes in at 404 GigaByte (as expected, it’s ProRes 422 HQ). Except the real movie is unreadable! Meaning the entire process is borked. Is there a way to repair this?