Multi tasking on iPad Air doesn't work fully

I am using an iPad Air md789x/b. IOS 11.2.6. Multitasking is enabled and I am able to move a second app up into slide-over position. When I pull down on that second app it will not go into split screen mode.

I have restarted the iPad a number of times. I've tried doing it on other iPads to ensure I'm doing it correct and yes it works for others, just not this one. Can anybody give me any suggestions as to why?