MKV files all of a sudden have stopped playing. I've changed nothing

All my MKV files no longer play.  I get the check supported files message.  I’ve watched several of these files many times in the past. I’ ve changed nothing that I know of.  They were working fine two days ago.  very frustrating.  Is this a common problem?  I searched the forums and didn’t really find an answer. 

Any ideas?  I’m not the most tech savvy person so ELI5  lol

have you tried resetting the hub using the button under the hub