Inside of P&ID you may notice that the selection list from the substitute component grip is blank. Although you can still choose and swap out the components the geometry of the symbols does not display.
This can be fixed by first closing your project. Remember that closing the software does not close your project. In order to fully close your project, you need to right click on the top level of your Project Manager and select Close Project.
Once your project is closed, navigate to your project folder through windows explorer and locate the SubstitutionPalettes.XML at the root level of the project folder and delete it.
This file will be recreated when the project is re-opened and you should see symbols in your substitute component list again.