If you want to use EB Garamond as a custom font (with ‘Use custom fonts’ enabled), please provide a screenshot of the ‘Theme Options’ > ‘Fonts’ screen in your Admin Panel.
Some setting there seems to be wrong. My main suspect is the ‘Google Fonts extra subsets’ field. I guess you may have entered ‘EB Garamond’ there (which is font name, not a subset), and that is what is causing Google to return error 400 when being asked for the font.
By the way, if you want to revert to the original fonts, the best way to do that is to go to ‘Theme Options’ > ‘Fonts’, uncheck the ‘Use custom fonts’ checkbox and click ‘Update’: