Creo 9.0.0.0 missing parts when constraining

[ER_10745022]

I'm trying to constrain a part, but when I go into the constraints, some of the parts disappear. I need to constrain to these parts, so any help would be appreciated.

[pausob]

In Creo, the component that you are constraining can only reference already established components or assembly features.

Hence, all the model tree elements "after" the component you are constraining will disappear when you are editing its placement definition.

The solution is to re-arrange your model structure so that "parents are above the children" in the assembly model tree.