Sorry about your little buddy.
Have you been misting the tank? Any moulting arthropod needs quite a bit of moisture. Otherwise, the moult can turn out "bad"-- meaning the animal has trouble freeing itself from the old exoskeleton. I have seen tarantulas and crabs break their still-soft limbs off, trying to escape from their old shells. This usually results in the animal bleeding out or infection, and ultimately, death. If you find that your animal has broken off an appendage, dab the broken end with some clear nail polish, IMMEDIATELY.
Sometimes, it can be tricky, getting the moisture balance correct-- too much, and the enclosure will mould..too little, and your critters will dry up. What have you been using as substrate?
My old matriarch jumping spider passed last week. She was well over three years old, which is almost unheard of. They usually only live for one year, in the wild. I am heartbroken over her death.