Direct play suddenly not working - W10 Modern app

Hi,

I have been using Plex to play various file types forever on W10 and it has never faltered, but today I tried to watch something and it gives me the error “Unable to transcode video to a supported format”. Now, this is a video that I have played before, and is part of a season that has the same file types and which I was watching last night. I turned on logging and I can see a line that says something like “Direct play is disabled”, but it is not. I have reinstalled the Plex Modern app and nothing has changed since I watched another video in this series last night.

Any help would be much appreciated - I have about reached the limit of my, fairly minimal, expertise!

Although I have had no replies from this, in case anyone finds it, the Plex app is now livestreaming the offending files (which are .avi). However, after about five minutes, the livestreaming fails and I have to restart the video.