ios11 ipad splitview

For some reason, I can’t make any folders. Putting the apps together just makes the one app open or go to split screen. Am I missing something obvious? Am I doing it wrong, although I’m doing it exactly like always have?

Does anyone else have this problem? I'm at work using Notability and go into split view to check my email. I see my Amazon shipment has been shipped. Cool, lemme click on the shipping link and see where it is. Instead of switching my mail app to safari, it pulls me out of Notability and leaves...