It no longer does. When I tap it, the screen briefly flashes dark (like it was opening), and then it instantly closes. No error message is shown.
I'm running Rooted Stock MI9 (rooted with RDLV - MJ5 doesn't seem to have anything I want that justifies risking breaking a working setup), with Wanam, TiBu, Light Manager (paid), Keyboard Manager (to use hacker keyboard with terminal and ssh, and swype everywhere else), and Pen Window manager, plus some really boring, typical apps. No games, nothing other than the listed apps that does anything exotic.
It stopped working some time during the last several weeks. I have changed no settings during this time. The only app I have installed is Light Manager Pro (I previously used the free version, until a paid one came out), and I doubt this is the problem, but I have run normal app updates.
Anyone know what it is that causes this issue? I can still get to the battery and data usage screens from settings. It's just usage manager that doesn't seem to work.