Replaced the O2 sensor with a fresh new one from Vemo. I totally forgot that the Mini Cooper has 2x O2 sensors 🙂 Don’t forget that O2 sensors have a replacement interval which is usually somewhere between 160.000 – 250.000 km.
Update per 01-01-2021: I replaced the Vemo with a new O2 sensor from Magneti Marelli. The Vemo already started giving issues after a short while. It will be the last time that I will be using Vemo.