Them’s blisters.
How cold was it when you were playing? I once played on a (low budget!) carnival float at Christmas time (a local town Christmas carnival). After that and doing a few years of carols, I don’t think I’ll ever do it again. Playing outdoors (unheated) in sub +5degC is horrible (even if dressed as an elf). Hands start off cold, and only get colder from there.
You may wish to think about raising the height of your pick ups slightly and turning your amp up and playing with a much lighter touch, you might find that you get a sweeter tone like that from the flats - and your sound engineer will likely thank you (of course, you might have the best tone in the world already - impossible for me to know!

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