My apps keep randomly rearranging themselves

Is it possible that you or someone else using your phone is inadvertently moving the apps. I have done this multiple times on my own phone. If that is unlikely, try resetting your settings>settings>general>reset>reset all settings (no data is lost, but all settings are back to factory defaults.)

Resetting the home screen puts your home screen back to how it was out of the box. I also believe the other apps are alphabetized and removed from folders. I don't think it will help in your case.

I have the same issue. My apps will not stay in their folders and custom arrangements. They keep rearranging alphabetically, even while I am trying to put them back into their folders!

Ok. Hopefully that will take care of it, but if not there are still other things to try.

This happens to me too except they rearranged to alphabetical order. Anyone knows why this happens?

What do you mean rearranging themselves? If you have reset the home screen layout the apps will get rearranged.

The settings reset cleared up a similar app related issue I was having a few months back on my iPhone 6. Hopefully that will stick and solve it for you.

Follow the steps here to change back to a 4 digit code: http://www.macworld.co.uk/how-to/iosapps/how-change-ios-9-passcodes-from-six-dig its-back-four-3625836/

Consider trying a factory restore.