We had thought we were doing that, but this definitely got us on the right path.
We had to detach the objects and then copy/paste them outside the container to create a new object for each chart without losing any settings, then just recreated the container with the new objects.
It looks like the original creator had deleted the objects after putting them in a container for cleanup, not knowing it would cause issues. I moved new objects to a hidden sheet instead, so hopefully this prevents this happening again. I'm just glad I didn't have to try to recreate all the charts.