XC60 Rain Light Sensor Fault

That sounds remarkably similar to an issue I had with my previous Renault Megane. Different brand, but the symptoms were almost identical: problems with the automatic lights, wipers acting up. Check the sensor itself for any physical damage. Is the sensor area on your windshield clean?

I inspected the windshield area around the sensor, and it appears clear. However, a closer examination reveals slight bubbling underneath the gel pad. Could this imperfection be the culprit behind the sensor malfunction and related electrical gremlins?

That bubbling under the gel pad sounds highly suspicious. In my case with the Megane, that was exactly the problem. Moisture was getting in and affecting the sensor's readings. It's not something you can easily fix yourself. I'd recommend taking it to a workshop. They'll likely need to replace the sensor or at least reseal it properly to prevent further issues.

Following your recommendation and a workshop visit, you were spot on. The bubbles under the gel pad were interfering with the sensor. A replacement and recalibration costing 62€ resolved the issue. Thank you for pointing me in the right direction and saving me from unnecessary troubleshooting!