I have just upgraded from Windows 7 to Windows 10. (I never had this problem in Windows 7)
My Setup: Left Side 22" 1680x1050; Right Side 24" (Main Monitor) 1920x1080
They are aligned so that the top of both screens are on the same height. But when I try to move my cursor from one screen to the other at the top of the screen the cursor gets stuck in the corner and I have to move it down a few pixels (like 10) to be able to move it to the next screen. Same thing on the bottom of both screens.
They are aligned so that there is a 0 pixel gap between them according to Display Fusion.
Even changing the position so one monitor is way higher doesn't fix the problem of the cursor getting stuck in a corner.

Could this have anything to do with my Windows 10 settings? (I did a direct upgrade from 7 to 10) Or maybe something in the AMD Crimson driver?

Apperantly this is a Windows 8 and 10 issue and not a Display Fusion problem.
I found this post:
http://superuser.com/questions/498576/how-to-disable-sticky-corners-in-windows-8
And fixed it with the tool recommended in above post:
http://www.jawfin.net/?page_id=143

In my opinion it's a feature. It helps when I attempt to quickly move my mouse to the top right corner of my left monitor, aiming for the close-window button: it prevents me from going too far.

But, I could see it being annoying in certain situations.