Sleep mode stopped working after reset
I have iPad 2 and i resetted it to factory settings. After setting it up again I recognized that iPad does not go to sleep anymore from power button. I tried also sleep it from AssistiveTouch-menu but that does not work either.
Then I tried to reinstall iOS from DFU mode with iTunes; no effect.
When problem revealed first time I had iOS 9.1 in it, yesterday I updated it to 9.2. No effect.
What could be the problem? I would understand if I had something like dropped it, but I just resetted it. Could it be still hardware problem? I prefer more to software bug, but what do you think?