Why my goldmine doesnt work?

[Dark_Moon]

My lv5 goldmine in zone2 usually stopped. today a friend buffed it with stadium snack, so i restart it.
But it still has Zzz on it.
What's wrong with it?
Does the lv5 stock below inflence it? it worked in past times.

[Robzy]

In the most recent maintenance, they fixed the bug where you could build mines and buildings overlapping, so now to make the mine work you have to destroy the overlapping building.