The problem is the back5
slot thinks it has a bounding attachment named 1
visible in the setup pose.
Do you remember how you deleted that bounding box? That would help us track down why the problem occurred.
Also, do you remember if you ever received any warnings when opening the project in the past?
Nevermind, we figured it out! :nerd: It is fixed in 3.8.87, available soon. Thanks for reporting!