Lead Developer
Hi Jamie,
If you have Jetpack’s Mobile Theme activated, it takes over the GP responsive styling completely, so the shift would be a Jetpack specific issue.
GP comes fully responsive without the mobile theme module, might be worth checking out 🙂
Documentation: http://docs.generatepress.com/
Adding CSS: http://docs.generatepress.com/article/adding-css/
Ongoing Development: https://generatepress.com/ongoing-development