Humm, i'm not exactly sure, but the way it sounds and looks is that basically every time you score you get money, so maybe when you reach that score it gives you less or none until you get higher again, so lets say i get a score of 1000, maybe you need to make a higher score like 1500 to get more money, kinda like its remembering your score and you have to get it higher each time for the money to continue to come in. But i'm not sure if thats the reason or not just the way it seems.
Well first off I personally don't play these mini games to "make" gold, I do them to refill my potion bottles, so normally I haven't run into this. Well until wednesday night, when I solo'd my way through counter weight east, west, and big ben. I just used a potion after ever battle to help speed up the fights. ANYWAYS I ran into not getting coin I think it was during big ben, it might have been counter weight west don't remember exactly.
Personally I think this is very lame, I mean it isn't like you make alot of gold doing these games. In the same amount of time that I did this game I could have killed some monsters for more gold and a chance at an item that gives more gold.
As to reset, I "believe" it resets the next day. I could be wrong, since I wasn't really paying close attention to it.