Instruments don't play the right notes sometimes, or it sounds glitchy (Muse Sounds)

When hitting the play button on a piece I transcribed for Oboe that is in Db Major, the oboe is not playing the transition from the accidental C flat to B flat note correctly, it just plays C flat all the way.
But it only does that with the new "Muse oboe sound" when I put it back to MS Basic it plays the C flat and then the B flat correctly.
I also have a similar problem for another piece in Eb Major for the Alto Saxophone, the sax should be playing a low E (true note : G3) but it plays the right note at first but can't sustain the sound and start to sound flatter and a bit glitchy. And it also only does that with the new "Muse sound".
I tried rewritting on another partition with longer note value for the oboe, and the same problem appears, I don't know why...
(Also when selecting the notes they sound ok, but it's really when hearing the playback there are some issues like sustaining the sound, sometimes the instrument don't play a note, etc...).