If you add new security roles on the Ignition Gateway while the Designer is open, the new roles do not show in the Designer until you either:
1 - Right-click the roles area in Security Settings in Designer and the click Refresh (as noted in this post), or
2 - Close and reopen Designer.
The first option works well, but is not particularly obvious (a refresh button as present in the SQLTags Browser pane in the Designer would make this more obvious).
The second option is a bit of a pain.
A third option would be helpful: automatically refresh security roles when using File->Update Project (or the associated tool bar button) in Designer. (As of Ignition v7.6.4 (b2013112117) | 32-bit, this does NOT refresh security roles.) I thought this button (“Merges any new changes on the Gateway into the open project.”) would do the trick before resorting to a restart followed by a forum search where I found the linked post above.