I started getting this today. My sim doesn't need to be stuck for it to start. The first time she had Get Stung in her queue and I didn't want to deal with it so I reset her and she held her pose for a while. Then later on she wanted to route downstairs to drink the water she'd grabbed autonomously and I reset her and it did it again. Then she asked her mom for advice and the mom still had the "be asked advice" in her active actions list even though the teen was routing off to do homework. I reset the caregiver and the teen still held her pose for a couple seconds.
I made a video messing around with it in a few scenarios. It's easiest for me to trigger it when she's routing to do something, and stuff she might do autonomously (dancing, getting a glass of water, etc) will hold longer than other things. It also seems like the game thinks she's still doing stuff while she's stuck--you can see she's already en route to go dancing after she unsticks at one point, and at the end she ends up in her room on another level even though there was nothing up there for what she was supposed to be doing. She'll reset normally sometimes like once she's already in the process of doing something (you can see that when she washes her hands, even if for some reason she walks through the stove to get there). The other sims in her household reset normally most of the time but I have gotten one other to stick doing the same things.
No mods or anything. The teen is a wizard, but her wizard sisters aren't nearly as sticky as she is.
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