Welcome to iMore. Let's see if we can get it rolling for you.
I just tested it on my iPad and it works for me. Have you checked to make sure that when you updated, the zoom setting in the Accessibility options wasn't turned off by default?
If it there and switched on, tap the screen twice and hold it, now move your fingers up the screen to set your desired zoom level without removing your fingers from the screen. At that point you can slide them up and down to zoom in and out to set the desired level for all future three finger zooms.
At the base level, three finger zoom won't actually give you a zoom until you set the level, so follow the above and see if it works and post back to let us know.