I met a strange problem when writing MIDI on Ardour. Some notes lose the sound ( or disappear quickly) and I don’t know why. It doesn’t work to remove them and create them again. You can watch the video to see the situation. https://youtu.be/wMeC0UKt2HI
Restarting Ardour solves this problem sometimes ( not always ). Using different instruments doesn’t affect.
It may help that one of the track is imported from MIDI, but it’s not the error one.
I use Ardour 5.12 on Linux Mint 19.03 64bit.