I am having the same problem for the past 3 weeks. System Info as follows:
11.5.0 Build 4235
Model # 3941RW ROKU Express 4K+
Device ID: S0AH219JDM6T
Issues exists regardless of the channel and usually (but not always) freezes coming out of a commercial break. Audio continues though.
HELP! I have tried router resets, ROKU resets, remote resets, cache clearings and anything else I can read up on. I never had this issue prior to 3 weeks ago and I have had this unit since last November.