With Scale at 100.0% on a 720p+ video, the Rotate filter will clip 1 pixel of height and width from the bottom and right of the source, leaving behind a cloudy or black border on two sides. If the video is rotated 180 degrees, the border is more pronounced and will show up in the top and left. The bug is part of Scale, because at 100%, an offset of 1 will migrate the border to the other side (kind of like moving carpet that’s one pixel too short). This bug can be countered with Scale set to at least 100.5%, either on the clip, Track, or entire Timeline.
As a side note, when a 1080p video is used in ShotCut (tho not with 720p), cloudy borders of 1 pixel are added to the top and bottom, yet the same Scaling trick of 100.5% gets rid of them. So it’s possible this bug is outside of the Rotate filter, and is compounded when the Rotate scale is applied.