Sorry for coming back to you so late and thanks for your inputs.
It started working again. But I’m not sure on what the problem was.
I have two possibilities:
1) Because of my work I’m using various softwares that have system-wide shortcuts (like Spectacle for window rearrangement). I have reinstalled some of them. Maybe these shortcuts for english keyboards had a binding that was not working with the Swiss keyboard.
2) Around the same time it stopped working, I have updated my Laptop. While uninstalling the softwares mentioned above, I updated the laptop again and also reseted the NVRAM/PRAM.
One thing that stands out (I don’t believe it was the problem though) is that the the bottom left of the chassis of the keyboard had a small bump in it. Between the alt and cmd keys. I flattened it out with my fingers but I don’t think this was the problem.