I mentioned this elsewhere but I'll repeat it here.
There are a couple of "gotchas" when rendering to video.
Here's the process I use:

1. When my song is ready, in the full Menu Bar at the top, > Save As > Save as video
2. When the "Make Chord Sheet Video" window opens, I IMMEDIATELY change the main BIAB window to
"Fullscreen Chord Sheet View" (with the smaller Menu bar)
by using CTRL+T (yes, both windows will stay open at once)
3. In the "Make Chord Sheet Video" window, I click on "OK - Render Video", then name and Save it
4. When the video has been completely rendered, I click the "Show Video File" button (opens File Explorer)
5. BEFORE I VIEW THE VIDEO, I close both the "Make ... Video" window AND the BIAB main window
6. Now when I double click the .avi file in File Explorer, the video opens and plays correctly

YMMV
Good Luck!
LLOYD S