Check your fuel sources even if they say they have ethanol free fuel. A local FBO (Northern WI) received a load of premium gasoline. A few weeks later my hangar mate's Cessna 140 (on wheels) swelled the inside of his fuel line. His engine stumbled on takeoff from Sky Harbor at the Duluth Lake Superior waterfront
. I checked his fuel when he got home & found it to contain about 5 percent alcohol. I then called the FBOs where he had been refueling lately.
One FBO called back a few days later admitting that on checking, their fuel was contaminated and that their bulk truck had delivered the wrong fuel
even though it was a certified load!.
The FBO then went thru their credit card receipts to try to contact everyone that had refueled from that batch but incredibly the credit card companies wouldn't release the names of the bad gas purchaser (security you know,,,,). There were 12 purchases they were unable to contact.
From that I'd say to verify that someone has checked each load for alcohol.