Stuttering playback after changing monitors

I have a MacBook Pro (15,2) which I use with a Dell U3219Q, 32" 4K monitor.

If I've been watching (local) videos on the laptop itself then plug it into the monitor and go to watch another video, it has a stuttering playback.  The fix it simple - to quit IINA and restart.  Or move it across to the laptop screen and back.