Possible if you submit a proper bug report that Funcom might be able to assist you.
However, this is an ongoing bug that has reoccured for some players. If I understand correctly, reproduction and/or solution has never been found.
Other than the possibility they may be able to help what he’d have to do is take down the building(s) and transfer the materials and all loot into unlocked boxes. Leave clan and both of you join a new clan. Access the unlocked boxes and take your loot.
You won’t be able to retain your followers with this method.