Percussion sounds have been turned into the sounds of different instruments
S3 - Major
Basically just produce a drum piece and then it comes up with a different sound.
e.g. on mine, the snare drum has the sound of a trumpet.
Score needed. Are you using MDL or any non-default soundfonts?
Probably a duplicate of #290147: Mixer not remembering changes in the channels, see also https://musescore.org/en/node/290349