An update on my situation:
Now the new account trick isn't working either. Test account one began to experience the recording bug while attempting another try at video capture. I set up Amphetamine before recording, and I assumed that is what was causing the bug. So I did some test recordings after closing the Amphetamine app and using the default power settings. The bug still occurs.
Went ahead and deleted test account one and created test account two. I'm encountering the recording bug on test account two right away with no third-party apps set up or running. Amphetamine wasn't set up and is disabled completely.
Apple support was supposed to give me a phone call yesterday afternoon, but the call never came at the scheduled time. Despite that, I will let the support chat know about my test accounts experiencing the recording issue.
As a last resort, I tried running QuickTime via terminal to see if any errors or messages appeared when the recordings fail. No such messages appear.
Frustrating....