I'm sorry but I think you can't solve that, instead you can avoid it.
Do the following:
Create again the geometry in Creo Layout, and again, use the group and ungroup feature. Now, save the file, but before close Creo, Save the layer display status using the button in the View tab.
Now you can close Creo.
Next time you open Creo, you should be able to edit anything you want.
Remember to check in the status bar, if the Layer status was saved.
