KGU 2:

Can't help you with the RB problems but I've been making BIAB videos for some months and never had a problem with the audio being out of sync with the video.

If they sync up in BIAB itself, they should be fine in the video.
I've been using the defaults in the Create Video window.

There was a point where I couldn't get the video to display AT ALL, only audio. Then there was a point where it would play the audio and video (sync'd) but would only play one "screen full" and wouldn't scroll.

I started a thread on this forum and got a ton of help, including info from Peter himself. You may want to do a search and see if you can track it down.

I'm talking about BIAB 2018, Build 520. Don't have 2019 yet.
Good luck!
LLOYD S