MIDI notes/tracks disappear

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.
Screenshot: http://www.squirrel.nl/pub/xfer/uploads/3CbYtDxN2MoZAVKtMzLZU99w.png

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.
Screenshot: http://www.squirrel.nl/pub/xfer/uploads/3C3Ztb6yw9BdKsDaidOpJiEg.png

Puzzled (and a bit frustrated since I lost a substantial amount of work on a real project).

Are the notes really missing from the data (i.e. not played) or just missing in the screen display?

Yes, the notes are still there. The display is gone (note that track 1 is shown differently, with thicker bars).

what happens if you select a track with missing notes and then press Ctrl-f (fit-to-full-height)? Can you see the notes yet? If not, grab the top and bottom of the scroomer (scroller/zoomer) in the track header, and expand the range of visible notes. Can you see them now?

When sufficiently enlarged, the MIDI ‘slider’ to the left appears. With this slider I can scale and move the track so all notes are in view again.
This even seems to persist when saved/restarted. Hoorray!

Just have the same problem here, except the notes are totally gone, nothing is playing anymore.
I imported a midi file into a new project, deleted some tracks just to keep drums and bass, recorded audio, saved the whole result, quit Ardour, come back, and no notes at all in the midi regions that were full just before quitting.
Ctrl F changes nothing, the notes are gone. The regions are still there. Some other notes are still there but they may come from other tracks, I’m not sure. It’s very weird. Even stranger, those midi tracks have patches stamps that I deleted with shift and left click, but they’re back.
Before saving and then quitting Ardour everything is fine though.

This is (1) a 2 year old thread (2) a bug report. Bug reports go to tracker.ardour.org and will generally be ignored in the forums. For us to work on a bug, we need a recipe to recreate it, which may include a session exhibiting the problem.