Is high humidity at night bad for cannabis?

65 and below is better. Lower than 65 definitely safer for late flower. That's when you have highest risk of microbial growth due to RH%. More plant material bunched up with less airflow, etc etc. one or two nights may not be an issue.. Keep eye out for bud rot if it continues... remove larger area than visible rot. pray it didn't spread elsewhere. It also impacts VPD in plant, which impacts rate of uptake of water. this could impact how concentrated you want your fertilizer. if it speeds up, you need to dial back a bit and vice versa if it slows down in the case of high RH. Temps are part of this equation too. def open vents at night if it reduces RH without too large of a drop in temperature. 70-80% is damn near an incubator for microbial growth with warmer temps.