Xorg sofware rotation refresh failure
If display is rotated using e.g. xrandr -o left, Xorg modesetting driver sends DRM_IOCTL_MODE_DIRTYFB containing 0 as framebuffer id and unrotated rectangle coordinates, stopping screen refreshes.
Due to this issue, ebook readers cannot be used in portrait mode if they have a landscape display (what is often the case).
See also: https://gitlab.com/postmarketOS/pmaports/-/issues/1721