Grounding is local only. Once that assembly is inserted onto another design that grounding becomes NIL.
Grounding locks the grounded component and ONLY the origin of the grounded component to the top level component.
It does not involve any of the subcomponents.
So you grounded the conveyor plate in the assembly, it became nil and then you grounded it again in the assembly file.
But you also assembled the support bars to a sketch located in the top level of the Conveyor Support Assembly. that sketch references the top level origin in that design and in that design that origin cannot move.
However, when you insert that design into another design that origin is floating and so do the three support bars.
YU can battel this two ways:
1. In the assembly design, also ground the Conveyor Support Assembly. I personally would not do that.
2. In the Conveyor support assembly, right after the first component is created (S-10062 Conveyor Plate) use an as-built rigid joint between that new component and the top level origin.
Then in the Assembly design, you can either just ground the Conveyor Support Assembly, or if that assembly is part of yet another assembly, use an as-built rigid joint (or rigid group joint) between the origin of the Conveyor Support Assembly and the top level origin in the assembly design.
If you consequently make sure that all of the origins in a design are involved in a joint your designs will behave as expected!
Thanks for taking the time to create these files. That makes support a lot easier!
Model is attached,