Musescore on an older MacBook Pro
I have Musescore 3 installed on an older MacBook Pro (mid 2010, OSX Yosemite, 10.10.5) and, although all the visual functions are working brilliantly, on trying play the notes written, the sounds are played several seconds after the highlight runs over the notes and there is significant distortion on some notes, causing subsequent notes not to sound at all.
Comments
I am just guessing here. Sounds like corrupt communication with the audio driver.
Go to I/O tab in preferences and hit "Restart Audio and Midi devices"
Have you installed any extensions such as the MDL (Marching Drumline)? If so, uninstall them.
https://musescore.org/en/handbook/3/language-translations-and-extensions
If all else fails, try resetting Musescore to factory settings: https://musescore.org/en/handbook/3/revert-factory-settings