Invisible notes and many other bugs after importing a simple MIDI melody

– Export MIDI clip from Ableton
– Import .mid to existing Hookpad project
– Try to add notes to imported measures via Hookpad UI

When I try the last step, notes are invisible, but still play. When I add notes to a new measure, notes appear, but note pitch and length cannot be changed once placed. When I try to change the length of a note that was added after the imported section, it changes the length of a seemingly arbitrary note earlier in the arrangement.

This has made my file completely unusable…