Please psot the specific score you are having problems with.
It sounds like perhaps you tried creating a score for an instrument other than drums then changing it to drums later in the Mixer, but this does not really work. You need to create the staff as a percussion staff in the first place in order for everything to work properly.
Closed due to lack of information. Please report, with precise steps to reproduce, in a new thread if this still troubles you in the latest version (3.4.2).
Comments
If it may be useful to you, and you have not already done, take a look at the links on this conversation: https://musescore.org/en/node/65101
Please psot the specific score you are having problems with.
It sounds like perhaps you tried creating a score for an instrument other than drums then changing it to drums later in the Mixer, but this does not really work. You need to create the staff as a percussion staff in the first place in order for everything to work properly.
Closed due to lack of information. Please report, with precise steps to reproduce, in a new thread if this still troubles you in the latest version (3.4.2).