Not clear which model you have, but if you dont have the latest RokuOS build (9.4.0-4200) released for all devices yesterday, get it now (it may address this issue): Settings/System/System update/Check now
StreamerUser Roku Community Streaming Expert
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I am attaching some pictures that makes the problem clear. In 1080p mode, the displayed content is disproportionate to the size of the screen. You can see from the attached pictures that a significant portion of the content is not being displayed.