Screen Shot Problem

Hi. It still works the same as before. Briefly click Sleep and Home buttons together. Do not hold them. There is a rather long delay before you hear the camera click and see a thumbnail of the image. This delay is new, and may throw you off.

Sorry. I just enabled Assistive Touch on my iPad Air with iOS 11.1.1. Screenshot works fine that way as well.

Have you tried restarting the iPad? Power off, not just sleep.

You may need to take your iPad to an Apple store for assistance. Make an appointment.