So the button was grayed out and that's why I couldn't click it. As for answering your first question, it's hard to say. It usually happens after I complete a round. I'll place the toilets but it won't become clickable again. I want to say this happened without toilets once but I can't remember. I do know it's happened to me after rounds 3-8. The button is grayed as soon as I enter the end of round screen and place the toilets, so it had nothing to do with placing symbols or multipliers.
The only thing all of these runs had in common, aside from my recent round 8 clearing run, was that I was doing extremely well. Like, "I have full x2 multipliers at the start of round 3, very few toilets at the start of 5, and I'm good enough to skip buying symbols and multipliers with my winnings" well. And the thing they all had in common was that they would have cleared round 8. Like I said before, it was always my incredibly good runs this would happen to, almost like corrupting the machine too much locks it down. That's why I thought it was a mechanic I didn't understand, since the corruption bar at the top seemed useless.
Thanks for making an addicting game! I don't have a problem. I can quit when I want.