It Has NOTHING to do with RH.
My plants go in temps from 80 -85
with r/h ranging 40-60 and have none of those issues.
Try keeping a room at 75 rh at temps of 80 or even temps lower slightly lower. For one carbon filters stop working after rh @ 70 rh being used constantly after awhile.
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Get a scope / loupe examin the plant leaf and look for bugs. If you see none great, you know its nutrient deficiency..
There are a good amount of charts out their that break down the symtoms of plants that are suffering
The general
NPK
Cal
Mag
and few others...