AutoCad Files should not be imported into Revit Project, they should always be Linked to have a control on the files.
- In Revit window go to Insert and Link Cad option for inserting cad into Revit
- Import cad option should not be used for inserting cad as importing creates issues while deleting or changing
- Linking CAD enables full control of the AutoCAD data in Revit project
When linking following steps shown in the image should be looked into.
CAD links can be reloaded, unloaded or removed from Insert > links>Manage links>CAD Links