Can you try switching deinterlace method from automatic to bob.
Bob - works with closed captions.
bob (half) - works with closed captions.
Advanced (half) works with closed captions.
Advanced (advx2) - screen flashes with closed captions.
I wonder if it's the gpu memory setting?
I am running LibreElec 8.0.0 on a Raspberry Pi 3.
When I enable closed captions on a 1080i ATSC MPEG-2 stream from Mythtv or TVHeadend the screen starts flashing. This does not happen on a 720p Stream or a 480i Stream. I think it must have something to do with deinterlacing at the higher resolution? 
This happens with both MMAL and OMX acceleration. If I leave the closed captions off, the stream plays normally.
this does not happen on Kodi on RetroPie on the Raspberry Pi 3, but I prefer LibreElec.
Also I have tried this both with a TV and a monitor and it does the same thing.
Any help would be appreciated.
Thanks! 
