Warning: this is one of those vague bug reports again. Really sorry. Fortunately, there's an easy workaround for now. So, IMO, no need to really investigate intensely. It's still happening every now and then so I'll report back if I notice more things.
THE BUG:
Sometimes, the play button doesn't work correctly. The play button shows that it's currently playing, but the timeline doesn't go forward. As far as I've noticed, it gets stuck at 0. I'll have to pay attention if it also gets stuck at any other point.
I think it happens when looped playback is turned on. I'll try to pay attention to that detail too and get back to you on it. But it does make me suspect that it thinks the start and end of the loop are at 0 and 0.
SOME THINGS ABOUT MY SETUP:
I have 3 skeletons in my project. But I've turned off the visibility dot of the other two (they're two additional effects things that follow the main skeleton along in the game). I also have no animations selected on the two other skeletons when this happens.
THE USER WORKAROUND:
Whenever this happens, I turn Looped Playback off and on by pressing CTRL + R twice. Then it plays normally again.