Process log and error dump...   2018-03-01 12:17:33.179 proximity[52803:1213501] Unable to register font: Error Domain=com.apple.CoreText.CTFontManagerErrorDomain Code=-1 "Could not register the CGFont '<CGFont (0x7fcc9b582060): CiscoSans-Thin>'" Use...

Same issue here. Just began happening. Don't have a pinpointed date, but same symptom - unable to load the font.