I think I’ve fixed this problem.
I realized that the two videos which were freezing were also played as examples in my experiment instruction routines. Even through they were different objects, the fact that the examples and the trials used the same video resource seemed to be causing the experiment to freeze on the second playback.
I followed the instructions in the thread below, adding a code object which runs “myVid.reset(); myVid.play();” at “Begin Routine” and myVid.stop(); at “end Routine”. As far as I can tell, this has resolved the issue.
It seemed necessary to add the reset() routine right before the play() routine in my case, although in the thread it says that play() should work by itself.