This bug still alive, in UE 5.1 from source compile ue5- branch
My child blueprints of a common parent, have all their inherited static mesh reseted to parent setted mesh.
I try set the mesh at it, save it works in editor, but as soon i restart editor or reload the blueprint asset its gone! 
It started happen suddenly, and only affects this specific blueprint hierarchy.
If i create a new hierarchy from actor base, it works normal.
So i believe this blueprint asset become somehow corrupt and always get it value reseted at the 3rd level hierarchy and above
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