Drumset Unpitched - buzz rolls not playing

Not sure what a ".mdl" file is, but MDL in the MuseScore world stands for "MuseScore Drumline:, a free extension you normally would download via Help / Resource Manager, although currently you might need to download it manually. See https://musescore.org/en/mdl for more info. You need that extension, or at least the soundfonts it contains, for the buzzrolls to play as such. But I don't know that there are any actual files whose names end in a ".mdl" involved. Different meaning of the word "extension" here - MDL is an application extension, not a filename extension.