I have had the same issue recently. My Sim was also T-Posing and resetting herself everytime I've tried taking off the necklace. It kinda got me a little frustrated cause I thought I had to craft the jewelry again, but then I figured something out: If the jewelry is locked in your Sim's inventory, you can still go to CAS and remove all the accessories there. That solved the issue for me, hope it works for everybody else ever encountering this! 😇
Also make sure to check every outfit type (from Everyday to Cold weather outfits)
