Can't hear pitches consistently when using mouse to click notes in staff

Let me start by saying how much I love Musescore, and how appreciative I am for the work of others on this great project!

However, since the upgrade, I have issues more frequently.
Situation: I've entered and saved a score, want to modify some pitches here in a measure, and "fish" about for notes without going to my piano in the next room. (no midi keyboard), Accomplish this task by mouse clicking on the notes on the staff. Used to work 99% of the time. About half the time now, I click on something and it simply doesn't respond. The clicked on note appears darker in color, but no playing action.

Possibly similar, will use the playback function, and want to pause it. Click pause. It pauses for a moment, then resumes. Very maddening, cuz you can't edit til playback is successfully terminated.

Any ideas of what might cause this? Thanks!