instrument track missing from session

Cubase 10.5.20 Pro on Windows 10 Home 1903.

I opened a previous session and was missing an instrument track containing Groove Agent SE. I was able to recover some of it by importing the track from the latest .bak file.

This happened one other time where all MIDI data and instrument tracks were gone, which I didn’t report at the time.

If I provided the .cpr and .bak files could they be compared to determine how the track was removed? Could a project file be corrupted but still open?