Failed to merge bones with modified mesh

Hi! I’m trying to create equipment meshes for the characters in my game. I have made several already but just now it doesn’t seem to work any longer even though I’m using the exact same method.

I’m using the same mesh that the character has but I modify it to create the equipment pieces. I’ve made three so far with no problem but now I get this error message:


The skeleton of the modified mesh is identical down to every detail but unreal seem to think there’s a “significant change” to the hierarchy. There’s no change at all to the skeleton so I’m not sure what the error message is refering to. Can someone explain what the error message mean or how I can troubleshoot the problem?