I posted a question in the swamp but thought I would post it here also to see if maybe you all might have some ideas.
From the swamp:
I have had several incidents in the last several months where the default thickness in a multi body sheet metal part was changing & changing the thickness of individual body thicknesses on me and I could not figure out what was happening. This also caused us to create incorrect parts due to not noticing that a thickness had changed.
We believe it has to do with relations and/or merge bodies. I have discovered that if I create a new sheet metal body with a coincident relation to one of the bodies, the new sheet metal body will automatically show a default thickness of the related body, not the default sheet metal thickness of the part document. If the thickness shown is the correct thickness for the new sheet metal body and the user clicks ok all previous created bodies that have their thickness set as default will have their thickness changed to the new bodies thickness, which then becomes the new default.
Link to swamp: