Maybe this has already been reported, but a search reveals a number of problems that may be related but no solutions.
It concerns the pitch of unpitched percussion: a contradiction in terms. The problem manifested itself as percussion from a new soundfont being visible on the vu-meter but inaudible. The suggested cures for similar problems I found in the forums were of the form “get better loudspeakers” etc.
This might have been a partial cure but it would also require bat's hearing - the sounds being produced 5 octaves too high.
The cause is what appears to be a serious bug in the synthesizer. My reading of the SF specifications is that if scaleTuning, coarseTune and fineTune are all 0, then the sample is reproduced without any pitch shift. This certainly seems to be case for at least some synthesizers, such as Coolsynth and Timidity. But it is not the case for the synthesizer in MuseScore.
The specification for scaleTuning is that “A value of zero indicates that MIDI key number has no effect on pitch”. The implementation in the Musescore synthesizer is subtly different “A value of zero is taken to be the default value of 100 with a constant MIDI key number of 60”
This will give equivalent results if and only if
byOriginalPitch is 60 or 255 (-1) and overridingRootKey is unset or -1, or
overridingRootKey is 60.
As a number of soundfont editors arbitrarily preset byOriginalPitch to 60 and not many people are prepared to spend the time required to set up their own soundfonts, this problem may not manifest itself very often.
If, however, byOriginalPitch is set to 0 (a perfectly valid number, the nearest to the recommended value of -1 which not all soundfont editors allow) the sound is produced 5 octaves too high (middle C ~8 kHz at the limit of audibility).
Many soundfonts, do not use a scaleTuning of zero, but use overridingRootKey (e.g. TimGM6mb) or byOriginalPitch (e.g. Musyng Kite) to “tune” every note so these are unaffected by the bug.
The workaround is somehow let people know that they need to set byOriginalPitch to 60 for unpitched percussion in Musescore.