My part is missing one of its internal faces. The face was created by cutting a hollow out of a larger solid, so I can't select the face itself in the tree or anything.
I've seen elsewhere that there is probably an error caused by my use of fillets, and probably freeform. However, the face is symmetrical to the opposite side, which shows fine.
I read about it here: Missing face on solid body
I'm having trouble finding my error though. Any ideas?