NOTE: I do not expect an answer to this, it's just something weird that I thought I'd note.

I finally did the final renders of my big project (sadly NDA prevents me from any specific information), I ended up using HVEC for my intermediates before converting to x264 using a transcoder. It's done except for some short works (trailers etc).

But on one of the projects during the credit roll (the last... 45 seconds really), it rendered it a really really low resolution. I've rendered this project (at various stages of completion) probably a dozen times with this exact rendering profile. I did an immediate re-render with no changes, same issue, same spot. (It looks like the resolution and bitrate took a nosedive to like 240p level, which with text is even more noticeable.)

I worked around it by doing a loop region on the credit block and that rendered file (same project, no changes!) and used an non-reencoding cutter/joiner to put the credits on the original render (somewhat cheesy but it worked.)

Weird.

Vegas Pro 15.0 (Build 384)

(If it ever happens again with a personal project instead of a professional one I'll happily share clips/info.)