Thanks for your response and sorry for my delay—WP didn’t alert me there was a response—but I actually figured this out. It was the adaptive images plugin we’re using that was automatically resizing all images over 1400px down to 1400px, rather than something within WordPress. Thanks again for your response.
I spent a while refreshing and deactivating/activating it throughout that day and it never started working; however, I’ve reactivated it now and it’s working. Very strange.
