I have seen their ice cream machines start working more and more frequently. It appears there is a direct correlation between which locations pay more and which locations have ice cream. (Investigation ongoing)
Most of what I always knew from employees was it was something that was a pain to clean so they would want to start early (preclose) to make sure they could get out quicker. Then eventually some would close it earlier and if sales were low on ice cream they would lie and say it was broken so they wouldn't have to use it all.
Can confirm. On more occasions than I could count my manager would be cleaning it or having just cleaned it, and would tell anyone on the register not to sell ice cream until the end of the shift because it had to be clean for overnight.