I did this again (822), followed my previous steps, and hey, it worked.
Then I proceeded to:
- change AutoFix to Chords - fine
- select a new best RT - bang, BIAB stopped working (Not Responding)

My view, after playing around with this for a while now - BIAB has a problem at certain combinations of Autofix and selecting new RTs. It might take 3 or three RTs before it hangs, it may take changing Autofix from Song to Chords...

It's perhaps not something that users will generally do a lot, but as far as I can see, BIAB in 822 will crash (Not Responding) pretty soon after performing the 2 actions above.....