To make Divi (and themes based on Divi, like Extra) work with OMGF or OMGF Pro make sure Divi > Theme/Plugin Options > General > General > Use Google Fonts is enabled. OMGF (Pro) replaces Google Fonts on-the-fly. Which means it needs to know where Google Fonts are located in order to replace them.
Divi's big update introduced many changes; how it handles Google Fonts is one of them. You'll have to disable the improve Google Fonts loading setting under Divi > Theme/Plugin Options > Performance to make sure OMGF (Pro) is able to detect the fonts.
The Extra theme also offers the same features as Divi, the options to disable are located under Extra > General > Performance.