I've been struggling for quite some time with what seemed to be a random bug.

As you can see on this page the video player is loaded but no controls are available whereas on this other page it works perfectly.
Without errors in the browser console I had to dig a lot to understand that in the first case, captions are not available at all (not even auto-generated ones so the button is disabled on the Youtube player), while in the second case auto-generated captions are available (on Youtube only, AblePlayer doesn't seem to support them for now).

I hope this gives you enough context to find a fix!
Feel free to ask me if you need more info.