How to reproduce:
1. Create a new LWRP project
2. Create a new PBR Shadergraph and try to open it, observe that there are no issues with opening graphs
3. Close the graph and remove the LWRP package, observe that the graph lost its icon and is no longer openable (This is expected since the package has been removed)
4. Reinstall the LWRP package and try to open the graph again

Expected result: the graph is opened without issues
Actual result: the old graph has a proper shader graph icon now yet it is no longer openable, rendering it useless

Reproduced with: 2019.3.0a1; (LWRP/Shadergraph version 6.5.3 & LWRP/Shadergraph version 5.2.3)
Not reproducible with: 2019.2.0a14 (LWRP/Shadergraph version 6.5.3 & LWRP/Shadergraph version 5.2.3) 2019.1.1f1; (LWRP/Shadergraph version 5.13.0)

Note: Restarting the Editor does not fix the issue. The bug does not occur when updating an existing package only when removing it and then reinstalling.