Playback of File skips, black screen/no audio

I have been running Plex and emby media servers and playing back with Rokus. 

Current model is a 4802-CA.software version 12.5.0 Build 4178-C2

I have almost 2800 episodes of content that play perfectly - no problems,  But one show recently started - not stuttering but just dropping the picture and sound so about 2 seconds and resuming play as if it was playing the whole time.

I have recoded the files several times using different encoders (Handbrake, NVENC, Quicksync) and formats but it does it on MKV,  h264, and h265.  I even tried recoding from an MKV in case there was metadata in the stream but no joy.

It is not network related.  The Roku is 4 feet from an access point, it is connected to 5GHz, 522 tx, 866 rx.  The access point is wired 2.5 Gbps to the router, and so is the server.

I have no errors from Emby.  The file is direct playing from a 2.05 Mbps stream with one passthrough audio track.  I have played the files in question on Emby on my Google TV and android phone and they play flawlessly.

The only thing I have found that stops the skips is coding the file with a set frame rate 30 frames a second.  Because its animation - this creates significant artifacting.

The problem started suddenly but as I have adhd like symptoms from an anxiety disorder I can't link it to an update or other changes.