Question whether preheating even matters enough to fight about. People act like skipping it is some kind of crime against the air fryer gods, but it is just a tiny oven with a fan. My sister preheats hers for everything, even toast, and her food comes out the same as mine. Sounds like your dumplings were splitting because of steam inside, not because the basket was cold. Hot air hits frozen dough fast either way, so the preheat thing is mostly habit.

Honestly that sounds so painful, 11 hours for one clogged hole would have me throwing tools across the shop. Been there with my old rivet forge too, weak fire drove me up the wall for weeks. Turned out a little chunk of scale and ash had baked into one of the air holes and I never spotted it until I poked through every single one with a wire. Ngl it makes you feel dumb after but you learn to check that first next time. The clinker buildup is the real tell, that stuff loves to collect right where the air flow gets choked off. Glad you finally got it sorted, those tiny gremlins in the tuyere are the worst.