Second bug of the day
Second time I see this bug
Won't post the file because it will always happen on a different location for every file, making a generic solution mandatory.
It's not missing the base plane
I zoomed out a lot
Every dependent sketch is shown (although I know that the cause was a missing plane with no sketches)
I deleted all the lines on the problematic sketch, leaving a single one, and the problem insists on staying there.