GarageBand: Midi-Files don’t work with guitar presets

whenever I import a midi-file into GarageBand (10.1.2) it works fine until I want it to be “played” by a guitar preset. The only guitar that will play the midi-file is the Classical Acoustic Guitar and any other instruments work fine. I get no error messages and nothing is grayed-out either, there is just no sound and no movement on the volume bar.
I tried to play the exact same notes with GarageBand’s own midi-keyboard and that works fine, but it would be tedious work to replay the whole file since the files I’m trying to get to work were created with a different program (TuxGuitar).
I tried restarting the MacBook and I tried using other midi-files. It only once worked whenever I went back into a project file of the same day in which I changed the bass preset into a guitar preset – but that has never worked again since.

I hope anyone would have an idea of what I could do. Many thanks in advance!