I found the reason for the holes in the contest lot. I made a mistake in the code that should exclude contest lots from being reset. Since the contest holes are not aligned with chunks, the reset function shot some random holes into the area. Very sorry about this.
Good thing is that the reason was actually trivial and could be fixed. If the teleporting there would have caused this (it caused some severe issues before, such as server crashes). we would have a much harder issue to fix.
So thanks to all who suggested solutions and tried to help here, and sorry again.