Facebook videos no longer go full screen on my iPad Air

For some odd reason Facebook videos will not change to full screen as before. I tap on the diagonal arrow in the lower right corner of video to make it full screen but now that doesn't work at all. I checked everywhere for settings but cannot find anywhere that would prevent that from occurring. It used to do this but now nothing happens when I tap on arrow.

Frustrating that things change for no apparent reason and you can't find an answer.

[Re-Titled by Moderator]