When touching a video on WhatsApp, even it has already finished downloading, it will open the video showing the pause button in its center as if it's opening, but it won't start.
Some videos do play well, some don't. Anyway, I get no error messages.
I can only play the videos from the Gallery.
This answer on WhatsApp's FAQ, apparently talks about a scenario where the videos cannot be played at all, whereas in my device that can't be played only by WhatsApp.
Even videos I recorded in my device within WhatsApp, won't pay on WhatsApp.
I reinstalled WhatsApp (losing much info on the way!), but that didn't help either.
I'm using WhatsApp ver. 2.18.65 on my Asus Zenfone 2 with Android 6.0.1.