I have no idea whether this will help, for sure, but based on the possible sidetracking of your media stream by Roku's software so it can be identified, and information sold to advertisers, check the following:
Go to Settings > Privacy > advertising > limit ad tracking (check box to ON)
Again, Settings > Privacy > Smart TV experience > (uncheck use info from TV inputs; uncheck Enable auto notifications)
The rationale behind this is that these settings sidetrack your media material stream to provide Roku with saleable information. If the under powered CPU in your TV isn't working on this junk, it might actually be able to keep up with your actual media stream.
Let us all know how this works out.