showing mobile site on front page, and full site on others.

The front page is stuck in (what appears to be) a Mobile version of the site on my desktop. Other pages are displayed correctly, and the "live preview" and "customize" views are displaying correctly. When I click the "view full site" link at the bottom of the page, it reloads the same way. It has been working as recently as yesterday, and I've made no changes to the site between then and now. I really don't know if this is a theme issue, a WP issue, or something else? Any advice?