I have a policy in 11.0 with
No problem accessing the policy in the 11.0 console.
When I try to access the policy in the 12.0 Policy Editor, I get a Not Found message and am unable to edit it. However, I am able to delete it.
This bug is against migration, not the Policy Editor. Migration from 11.0 policies should not create 12.0 policies that cannot be accessed using the 12.0 Policy Editor.