Zero Turn Mower. I'm stumped.

I dont use anything but real 91 or 93 octane in everything , from mowers ,chainsaws,weed eater, leaf bower ,etc. , no problems , een letting them set for extended periods , humid/rain or not ..side note , run it in the 505 fish and the polaris too ...
Yeah, if I'm gonna put it down for the season, I'l run it out and put a tank of non ethanol AND Sta-Bil in it, but I normally run ethanol fuel in it during the season, because I was using it frequently, so it always ran fine, until it didn't.