High humidity despite dehumidifier in room - any advice?

62-63% is fine. Make sure that spike when temps drop never hits dewpoint. That'll be just asking for a mold issue. The dehum is too small.. need a bigger one. There's no other fix unless you grow fewer or smaller plants (i.e. smaller total canopy) The RH you target should mesh with your temperatures. Use a VPD table. Leaf temp is 3-4F lower than atmospheric temp, fyi. just stick to 65% or less.. if you need more it's better to reduce air tems than to go higher with RH. When lights go off, temperatures drop and "relative" humidity will spike.. your dehum must be able to keep up - whatever you choose to do. The plant closes it's stomata in the dark, so the moisture the canopy adds will be reduced at night, but that initial transition often comes with a temperature drop, which is the concern for RH spiking. VPD (temp and rh go hand-in-hand) is your primary concern while avoiding extremes for both RH and temperature.