In my site http://webdesign************.com/broadlands/
In mobile device, the headings are in Arial, and the burger menu is in Times New Roman. I have set them to Impact, but they don't change (you may need to check this on your phone, as it appears ok in the browser when resized). I have tried manually enforcing the font-family with CSS and tried adding the Impact font externally with font-face as well, but it just changes in a mobile device. I have also done a plugin conflict test which didn't help and debug log didn't provide any related information.