Assuming this is occurring on Roku DEVICES rather than Roku TVs...
Has anybody with this problem tried disabling the Auto-adjust display refresh rate setting? If your Roku has this setting, it is found here:
Settings > System > Select Advanced system settings > Advanced display settings
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
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Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X