The problem with the hi humidity levels can be anything from mold to the cigar swelling and splitting the wrapper during the burn or a bad burn , tight draw or tar build up. If you are at 75% and they are burning good I have a suspicion that you're hygrometer may be off. My other question is, how long have they rested at this 75% RH? A lot of time's a cigar right out of the box with out some rest and stabilization time in a humi will give you burn issues.