Ardour 5.12.0 (demo version from site), Fedora 27.
I start Ardour, create a new (empty) project “scratch”.
I import a MIDI file using one channel per track and default settings.
I save the project and exit Ardour.
I start Ardour, and select project “scratch”.
Track 1 has lost many notes.
All other tracks have lost all notes.
Puzzled (and a bit frustrated since I lost a substantial amount of work on a real project).