I cannot tell for sure, but your threads also look a little deformed so the nut could have simply got stuck on the threads. Dirt, Smashed Threads, Bad luck, the outcome is all the same. The prop cones are terrible for staying on (not a lock nut) and usually cannot use a wrench of any kind, but they do help protect your threads in a crash
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Make sure you aren't cranking too hard as well when tightening the props. These aluminum prop adapters can only handle so much so many times.
But yea, carry an extra tooth brush or gun cleaning brush and if you cake your threads with dirt, give them a quick scrubbing to remove the dirt. If the threads are smashed, you could probably run a die down the threads to reform them enough to allow the nut to come off without snapping the stem as well. But I wouldn't carry a tap and die set, I don't even have one
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If it makes you feel better, I have done that to steel bolts when using too big of a wrench, too much torque and the metal simply twists off as you see there.