Group members had to be "moved to the project"

[tranduytankts]

Hello everyone,

I am having an issue with grouping. That I have a few 2D imported CADs. When I select all and group, it’s still fine. But if I edit group and remove one CAD, I cannot add it back to the group. There is a warning and button for “Restore All Excluded” appears. Does anyone know the reason behind it? Thank you in advance for helping me

[pyXam]

This might be the wrong forums for this question.
Unless you are trying to do so within Dynamo for Revit?