Plug in changes fonts in admin

I’ve installed the latest version of this plug in on a multi site (individually activated, not network activated) and it’s changed the font in the admin area from Open Sans to what looks like Arial (I’m not font expert but it definitely changes when I turn the plugin on or off).

The menu is unaffected, but the font has changed in everything else.

Definitely this plugin is causing it.

https://wordpress.org/plugins/freshdesk-support/