I've been having an issue lately. I have videos I recorded off of VLC Player on my PC and uploaded to my Drive account. I downloaded them to my phone, a LG V10. Under Properties, the format is listed as "MPEG-PS". Originally they just worked on MX Player. Then at some point they started being "not supported", so I had to download some custom codec thing. That fixed it. Then a while later, it stopped being supported again, so I had to download that aio custom codec. That made it work again. Then just a couple days ago, I got my current issue: I can play the videos, but can't zoom, pan, change the aspect ratio. The bottom right button that controls these functions, as well as the touch screen buttons, just do nothing. The videos are stuck in a stretched out aspect ratio while vertical, but normal while horizontal.
It's not relevant to codecs. does it happen with all videos? Can you just reset the settings of MX Player & check again? If the problem persists, kindly collect a bug report immediately after reproducing the issue & share with us. It will help us to understand the issue better.