If I remember correctly, BIAB had a problem with ASIO for a while. I owned BIAB since 2014 or so and always used it as a backing track 'tool' whilst simultaneously playing guitar through Line 6 software modeller or Reaper with some VST amps.

This all worked great using the Line6 ASIO driver until one day when it stopped working. This was incredibly frustrating. I am not 100% sure if it was a BIAB problem though.

A year later, perhaps with BIAB 2019 it started working again. If you do a Google search, there are actually a few posts from 2018 in relation to ASIO issues.

It all works great now, I still used BIAB in ASIO mode playing my own backing tracks, plus the guitar through Reaper and a Line6 VST modeller.

If it's within your means, I suggest to consider an upgrade. Perhaps install 2021 in trial mode for a few days to find out if the problem still exists...