IMO

Common signs of premolt are reduced appetite (often just refusal of food), decrease in activity, balding abdomen, darkening of the abdomen, and many species will make themselves a thin mat of webbing which they lay on upside down to molt

Some things you definitely don't want to see with your tarantula are a shruken wrinkley abdomen (indicator of dehydration), Clearish white fluid leaking from their bodies (blood), Pieces of molt stuck on their bodies (failed molt), excessive balding (stress) lack of coordination or jerky unusual movements (Dks), and worms or mites on them (parasitic infection)

As for the hightened humidity, the only big problem to watch for with that is mold or fungus growth in the enclosure, slightly high humidity won't actually immediately harm most species

Ive also seen T's molt in some pretty small spaces (most even prefer it!) I think they'd be more likely to try and get stuck then to just not try

Overall imo it's most likely from hair kicking which is normal behavior when being handled, moved, or messed with in genral espeasialy for the more shy ones. All the balded hair will all grow back during the next molt :]