My problem is the opposite of this question. The task bar is auto hiding on my primary monitor just fine but it doesn't hide on my secondary monitors. Restarting didn't solve the problem. What is even weirder is I turned the auto-hide feature off and then back on the task bar on my left monitor stays up but it gets covered by a maximized window, the middle (primary) monitor auto hides as expected, and the right monitor task bar stays up and on top of a maximized window.
I'm currently running
Windows 10 Pro, Version 1511, Build 10586.104