I was playing on level 57 of the mobile version and for some reason I stopped making any gold. It has been at exactly 4100 gold since the start of level 57. I was attempting to upgrade the water tower at the bottom next to the black Smith to 4, and gold just stopped producing. You can see in the screen shot that I'm earning more points by killing creeps, but gold is not increasing. I guess I'm going to play for as long as I can without any income but this is weird. I'm on a galaxy S8