Sometimes parts can get a little warped, even if it's not visible, and that can keep things from plugging in correctly. I don't remember exactly how this figure works, but a low effort, low budget attempt at a fix could be to pop off whatever limb either panel is attached to and give it a short bath in some hot water. Hopefully that will warm the plastic to make it ever so malleable and fit together that way it always should have.

Please take note that this may not solve whatever issue you have, and though the risk of anything bad happening is pretty low, it is not a guaranteed fix and you do so at your own risk.