this has been going on for months and I have filed a bug report myself.
Sometimes, when you fill you main hall by collecting coins, the total doesn't go to full, but actually stops at one less than full. As a result, the ability to keep collecting further is not disabled, and the coins over residences and other buildings that provide coins (i.e. golden Abyss) do not "Grey out" as expected. If you do not notice the main hall is one-coin-short of full, it is possible to keep collecting and collecting until everything is thrown away. it happens in all a worlds, in all browsers, seemingly at random.
there is more at "#T11915525 Main Hall is not filling and greying out coin collection"