PMG gyms on the bigger cells are triggered at 2, 6, 20
So in theory, if there were 3-5 or 7-19, when the Gym Disappeared one of the others went from a stop to a Gym and then when it was restored (either by new submission, or someone monitoring this thread) the cell was full so it became a stop.
Now if there was 2 or 6. It might have triggered the random and something else became one.
Now, the worst case is if there was 2 back in day that triggered the Gym, then the other stop was already removed, Gyms don’t downgrade when you go back to 1… BUT if the other one was already removed, and then this one put back its now the first/only POI in cell so a Stop.