BP multi-level inheritance does not correctly inherit 'Static' mobility

User reported an issue of a mesh not being visible when a project has multi-level blueprint inheritance. After reproing, I believe the root cause is DefaultSceneRoot of the grandchild BP class not correctly inheriting Mobility of the grandparent class, or that Mobility being modified during loading. This in turn affects the attachment process of the DefaultSceneRoot child StaticMeshComponent. UDN case linked.

• Create a new actor BP_A
• Add a static mesh component and pick a mesh asset
• Set both the static mesh component as well as the DefaultSceneRoot to static mobility
• Create a child BP_B based on BP_A
• Open the BP editor and replace the mesh asset with another one
• Create a child BP_C based on BP_B
• Open the BP editor and replace the mesh asset with another one
• Place an instance of BP_C in a level and save the BPs and the level
• Exit the editor
• Launch the editor
• Load the level with BP_C in it

Observe the DefaultSceneRoot's mobility in BP_C's has changed to Movable, rather than inheriting Static.