I am trying to uninstall CM Security. It's a device admin, so I go to Settings, Security, then Device Administrators, and try to uncheck the box next to CM Security, then a screen comes up listing the privileges the app has. The options are Cancel and Deactivate. When I click Deactivate, the button depresses, but it does nothing. I can click it as much as I want, and nothing happens. How can I deactivate a device admin when this problem occurs?
Try booting your device into safe mode.
You can do this by holding the power button until the shutdown menu appears, and then hold the "Power off" option until your device asks to boot into safe mode. There will be a watermark on your screen when you boot into safe mode to show you it worked.
When you boot into safe mode, only system apps are allowed to run. You should be able to deactivate the device admin from there, because no app can prevent the process from running.
Warning: all non-Google sync accounts are reset when you boot into safe mode (no idea why). This means you might need to enter your dropbox/onedrive/other account credentials.
There may have been a change to the app in the last four years that allows this: On my Android phone, I went to Settings, Security, Phone Administrators. Button Savior was listed as a screen lock with a checked box on the right. I touched the check box and the listing disappeared. I was then able to go to Apps, Uninstall/Disable Apps and press the Button Savior app to uninstall it.