Did you recently switched from http to https and having mixed content warnings like below?

Mixed Content: The page at 'https://www.domain.org/' was loaded over HTTPS, but requested an insecure stylesheet 'http://www.domain.org/wp-content/uploads/smile_fonts/Defaults/Defaults.css?ver=4.3.1'. This request has been blocked; the content must be served over HTTPS.

This is generally caused by incomplete SSL configuration and can be resolved by any of the solutions linked below.