An actual Whirlpool certified repairman came out to check our icemaker. It turned out there was an air gap at the top that let in room air which allowed water to condense on the outside of the water supply line and run into the icemaker and freeze. Making a big lump of ice and stopping the ice dispenser auger.
He pulled out the fridge, took a little cover off on top over the icemaker, caulked the gap(s), put it back in action and it's been fine ever since. He said he's seen this same issue several times. Apparently if they leave that gap at the factory then this icing up problem is likely to happen. His reports go back to Whirlpool so hopefully they've addressed the issue.