Mini Cabrio heavy steering and vibration

That sounds awfully familiar. Had something similar happen with my old Peugeot, although it was a diesel. Increased steering effort, vibrating wheel… turns out the steering angle sensor was the culprit there too. Does the traction control light come on by any chance? That's how it started with mine.

Traction control light hasn't come on, but it feels like the power steering is intermittently cutting out. You mentioned it happened to your Peugeot. Was it a sensor failure requiring sensor replacement, or something else? Trying to understand the potential depth of this problem.

Right, so with the Peugeot, the symptoms were almost identical. The angle sensor was sending incorrect data, which messed with the power steering assist. Luckily it wasn't a mechanical issue with the steering column itself, just a faulty sensor, like a bad signal in a wire. The workshop diagnosed it pretty quickly, and a new sensor fixed the issue. In your case, I'd recommend getting the error codes read to pinpoint the problem. Could be a coding problem, like you say, or an actual sensor failure. Either way, a decent workshop should sort it out.

Huge thanks for your insights. Turns out the steering angle sensor was throwing errors due to faulty coding. A quick visit to the workshop and a 195€ bill later, it's sorted. New sensor replacement was not necessary, they just recoded it.