Ouch. I’ll test as soon as I can, but this doesn’t look promising. It would be unfortunate. I have sometimes taken a BIAB song into MuseScore then exported it as Music XML. The reason is that sometimes the Music XML exported from BIAB gives an error message when imported.
I will try to find time to run some tests.
I have gotten the error message a few times importing the BIAB XML and just acknowledged it and kept going and it usually works out fine. But you never know! I use Musescore a lot, so hopefully they will get version 4 sorted out soon enough.