Key signature dissappears when clicking the UPD button

GIF (clicking on the UPD button when a note is selected)

nth time

For the nth time, make sure that all of the MIDI parts on the track are glued together!
I feel it’s time to write this on my forhead with a permanent marker.

GIF (what the problem was)


Interestingly enough, the key signature is in the second half of the split MIDI part.
Does anyone have any suggestions on what to look on a good permanent marker? :art: