Having a similar problem. 15" Macbook Pro, purchased in 2017, running Big Sur OS. A 27" External Monitor is connected via HDMI. After leaving the computer for awhile, I come back to find the display on the external monitor is offset, moved toward the upper right corner of the monitor, such that I can only see the bottom left quarter of the display. The display on the Macbook shows my sign-on. The mouse cursor is frozen on the external monitor. The only way to correct it is to do a forced restart.
pmcgill2970
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