Tricked by the AFR gauge.

So, how did you find the problem? I admit that would probably throw me off

It finally occurred to me that the motor wasn’t hiccuping and stalling or popping back through the intake.
It was a sudden on/off thing.
Then I finally realized the lean reading was from unburned oxygen.

I always carry a spare 8 pin module in the trunk in my little accessory box, so I swapped out the module and no issues since.