I am having this exact same issue with 2 different Rokus
Roku TV --> Model 40S305 Software version 8.1.0 Build 4060-08
Roku 1 Sold to me as the 2SE --> Model 2710X Software version 8.1.0 Build 4060-06
I have updated my server to the latest Non Plex pass version.
I have restarted my entire network.
Everything plays fine on any other platform.
This seems to have started after Roku Software update was applied to my devices automatically
Roku wants me to check content from another source (Channel) to see if this is happening there as well.
Has anyone else checked other content?
My PMS is running Version 22.214.171.12429
Operating system is Windows Server Essentials 2016
Please let me know if additional details are needed.