Sound files are a bit buggy
It appears as thought the bass clarinet sound files aren't playing as they're supposed to. The sound comes in slightly too late, and short notes sound TERRIBLE. I've talked to a friend who also has this issue, on a different computer, so I know that it's not just me.
This problem, of course, doesn't affect the written music, and if it really bugged me I could just switch it to a different instrument, but it's still an issue.
Comments
Work is being done to replace the clarinet sounds (see https://musescore.org/en/node/52271), but there are plenty of alternative SoundFont sample libraries you can try, available from https://musescore.org/en/node/36171#list. GeneralUser is a traditional favorite with MuseScore.