Mould ?

Yes, fungus..........just break it up with a stick or fork.......it is pretty well harmless. Pots are waaaaay too small for that sized plants.....transplant asap. 94% is incredibly high............cannabis is not a rainforest plant!

yap, those woodsticks are often bamboo which like to mold when it getting to wet 94% is pretty much alot, like tropical rainforests

bwahah didn't even see the hygrometer.. yeah you need a dehumidifier or exhaust outside... those tiny plants shouldn't be causing 94% RH, though... If that's the case now a full canopy will be a nightmare. will need a hefty dehum even for a small canopy if that is ambient.

Yeah.. usually not a problem when it's on the soil. Your plants are young and i'd wager it's a carryover from early on when you don't keep as good of a wet-dry cycle with nascent root zone. Light and allowing the top to dry between irrigations will clear up most ailments that are caused by early watering habits with seedlings. Sometimes you'll see algea too. usually the stuff on soil is absorbing any decaying biological material and not a concern for the plant in a direct way. With good watering habits it should die off.. could spritz it with a little 3% h2o2, too. I'd reconsider methods involving pruning off all the axillary grwoth. at least keep the leaves if no intention to use the branching. just slowing the plant down be removing foliage.

Its does certainly look like mold. It could be a case of slightly overwatering. And like Albinius wrote, lower the humidity, if that 94% is a true reading. One way to try combat this, could be letting the medium dry out a bit between waterings, to the point where the leaves start drooping a bit. And/or use an sulphur based remedy to help combat it, like House and Gardens Vitality plus.

Does your humidity meter say 94%? If thats the case it is probably mold. I would try lowering the humidity.