The quality setting may have reverted to something other than Original
The H264 Level may have reverted back to 1.0 - should be 4.1 to 5.0
Content may be interlaced - ALL interlaced content is now transcoded
or
Any number of other settings may have reverted - most conditions are able to be discovered with the use of:
Plex App Settings: Disable New Player
Plex App Settings: Display Information
Now when you bring up the OSD - Display Information will tell you:
Direct Play or Transcoding and if so - the reason.
What’s the reason?