OK, I figured out what changed.

In the audio setup screen there is a checkbox that says something like "use IM effects". Checking that box triggered the distortion problem.

The problem of the crashing was caused by the driver. I sent Focusrite support the information provided to me by PGMusic support, and they sent me a new driver. So far so good (no blue screens)

And it turns out that a bunch of other issues I've been having with RB were caused by file corruptions that were caused by blue screen shutdowns that were caused by the bad driver.

After getting a driver that works, and then reinstalling BIAB/RB from the USB drive, everything works again!