When I open a Library, some of the titles in my projects have been changing or resetting to a different font, usually Helvetica Regular. In one instance, the font reset from Futura Medium Italic to Futura Medium.
Not sure if this has anything to do with it but this problem only manifested itself after upgrading my OS from Yosemite to El Capitan. In one instance, the font I had chosen, GAZ, has disappeared entirely from the inspector. I can't even find it in the Font Book or Font Collection