Yours sounds defective, ive had mine since august and never have combusted. Ive also done 20+ bowls starting with dark abv going into black abv.
Abv is not inconsistent when used Improperly, there is an area that doesnt vape which I recommend putting a screen on the bottom of the tube.
I do have short tube and have heard the longer tube heats up quickly but you're the only person I've seen mention combustion.
I feel the flavor is fine until you reach 400+ temps (which is after like 3 hits), but I will agree that once its abv its all abv and it will taste like tube of abv.
But I do agree its my worst tasting vape, but I don't think the PAX is that great tastewise, yours probably would've been better if you replaced your long tube, max temp is 420 if you're getting smoke then its temperature sensor must be broken.