This is off the ROKU site-

Why is video jerky when watching a movie or video?
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When auto-adjust display refresh rate is disabled, your 4K capable Roku player outputs all content at 60fps. A movie filmed at 24fps, or a video shot at 25fps may exhibit subtle jerkiness due to the conversion to 60fps. To avoid this behavior, follow the steps listed above and enable auto-adjust display refresh rate.

I just ordered the ROKU Ultra. You can also use it wired with an Ethernet connection which gives the best connection and no interference, like Wifi can. If that doesn't solve my issue then I will return it back to Amazon where a bought my current ROKU Stick.