Part with external reference always requires a rebuild

Hey,

I have a part made as a skeleton part and for some reason it keeps asking me for a rebuild on one of it's skeletons.

The mate is a coincident with the axes aligned.

I have all the external references opened and unlocked yet it keeps asking me for a rebuild, no matter how many times I do CTRL+B or CTRL+Q

Anyone has any idea? I wish I could post the part but I'd have to post every other skeleton and I don't think my boss would like it if I did that.

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