Lost my apps file folder in iOS 11

Even under iOS 11, there is still a limit to the number of app screens (15 for my iPad Pro.)

I have downloaded more apps than can fit on these 15 screens, so the remaining apps simply don't appear, though they are accessible through Search.

To bring some of the hidden apps back on screen, I started putting existing apps into a folder, by dragging one app on top of another. I dragged about 20 apps into a folder this way and then the folder disappeared.