Poke around in the Accessibility menu of settings. See if anything is inadvertently turned on. There are a lot of settings in there that can be enabled. Actually some really useful stuff too I had no idea about until you posted this problem.
If that fails, try to clear the cache from the recovery menu. Or try to boot into safe mode and see if it's doing it there:
Instructions are posted here: http://thedroidguy.com/2015/08/how-to-boot-samsung-galaxy-note-5-in-safe-mode-wipe-cache-partition-p...
Let me know if these don't solve it. One of these might fix your issue though. If not, you'll have to head to a Sprint Store and have them check it out.
I'm just having screen issues with the top left. For example. When trying to delete a bunch of Text messages. I open it up tap MORE select DELETE. As I go to touch the ALL box on the top left. It doesn't respond.
And in other screens. I'm unable to touch the BACK arrow. And have to close out of the App screen.
A device reboot works but I shouldn't have to reset my phone 3-4 times a day. Because the top left corner goes to sleep.
Galaxy Note 5
take it into a repair store. they will need to have hands on with it to see what is going on. when you restart the phone does that top corner start working for a lil bit? it might end up being a dead spot on the screen itself but they have ways of testing this.