Touch ID: Fingerprint recognition suddenly got far worse

Without opening the device lately my fingerprint recognition suddenly stopped working. Well, at first I thought it stopped working, only to find out that the recognition got far worse.

Sometimes the recognition works on first attempt, sometimes I have to lift my finger up to twenty times until my fingerprint is recognized. And sometimes it doesn't work at all.

This is what I've tried so far:

1. Cleaning the home button
2. Cleaning my fingers
3. Rescanning my fingers
4. Doing a hard reset
5. Resetting the phone using iTunes
6. Opening the phone and checking all the cable connections

It has nothing to do with my fingers. Touch ID is working fine on my iPad. I've searched the web for anything like this without results.

Has anyone heard of something like this or has any ideas what to do to fix this? I'm out of warranty and I've repaired the phone on my own a couple of times so asking Apple for help is not an option.