Hello, friends. I believe that I have found a new bug to be fixed.
Namely, when I open one Musescore file containing several parts, and I open the mixer, and I choose to play any one instrument SOLO, without the others, and I close the MIXER window with the SOLO function still wroking, if I should happen to REMOVE any instruments from the score after that, such as by using the INSTRUMENTS menu item (except for the one instrument that was played SOLO), the end result is that I get no sound at all from the score, and it cannot be corrected. I must either invoke multiple UNDOS or else re-load the original file before the AUTO-SAVE kicks in.
I assume that the same issue will occur in reverse, if MUTE is invoked instead of SOLO, and instruments are deleted, permanently muting the instrument in question. I have not tried that one.