In the last couple of months I've noticed two performance issues that may or may not be related:
(1) When dragging-and-dropping a video onto SMPlayer, the video sometimes takes 45 seconds (or even more) before starting to play. This doesn't happen every time, but does happen several times per day.
(2) Often when a video first begins to play, the SMPlayer interface is completely unresponsive to mouse clicks. When I try to pause the video, no response; also, there is no ability to go to full-screen, etc. The player behaves as if the performance priority were High or Real-Time, even though the option selected is Normal. This can go on for as long as 1 minute before the interface finally accepts clicks. Sometimes I just use Task Manager to kill the MPV and SMPlayer processes.