Iphone 6s charging bug, or opening screen bug.

Hello There, I just purchased an iphone 6s, i have the last IOS on it.

When i m charging my phone, so my phone has the charger in it, i can not unlock it with fingerprint, i m just able to use the code to unlock it. So i have to unplug the phone to let the fingerprint works, in case i plug the charger back in the fingerprint, it doesn't work, It doesn't even say "try again " it just wont work.

Another bug is that when i unlock the phone, a black screen appear for one sec then dissapear. Just when i unlock the phone, exactly in the same time. I ve tried to make a screen shot, and i succeded somehow. After that it comes back to normal.

I want to ask it it's a bug from the IOS, or it s a phone problem ?