I had the last update fail as well. My problem was that I chose the "UPDATE" sub folder in BIAB as the place to download the update. It seemed quite reasonable since it was a BIAB update after all.
Well the update failed and BIAB was unable to back out whatever changes had been made. I couldn't start BIAB and I couldn't restart the update.

It seems that the "UPDATE" folder is not the place to store updates.

My solution was to recover the BIAB exec file from the original install, download the update again, but to the default download folder and then do the update. It worked fine, but why have an an update folder that can't be used for updates?


BIAB for Windows Version 2019 (643)
Windows 10 (1909)