I had been having a problem where my notification drawer would not pull down. At first, it wouldn't pull down at all. Then it would only pull down when I pulled from the very far left side of the notification bar. Then it would work if I was on the left half of the notification bar. Then only the left 25%. I tried rebooting several times, no luck. I switched to the marshmallow theme and all of a sudden it started working. I switched back to the standard theme, and it went back to the broken behavior.
I searched and searched and didn't find anyone else with these exact symptoms. I thought I'd have to factory reset to get this working again.
Fortunately, I was able to resolve the problem. Open system settings/general/apps, select the all apps tab, and scroll down to Home. Select it, and press the clear cache button. Now my notification bar can be pulled down from anywhere across the top of the screen.
I'm posting here in case anyone else ever runs into this problem in the future. I'm not sure what caused it. The touchscreen on that part of the screen was definitely working, because if I pulled down the drawer from the left side, then dragged my thumb down, right, and up, the screen was definitely responding to my finger moving around the very top of the screen on the right side. Something was causing the display not to pull down the notification drawer when I started from the right side.