Some buttons do not respond to touch

Some buttons on the phone do not respond to touch - for example the letter "p", the number "0" or quotation marks. Additionally, a circle with a cross to delete notifications in the Notification Center. This is not a touch problem because other buttons, if they are in the same place as the ones mentioned above, work properly.

I restarted the phone many times, removed protecting glass and the problem still persists.

Does anyone know what this is about? I admit that it is bothersome.