Hi Onno, it's solved.
I had downgraded the firmware to the stable variant, and this solved the issue. I was just testing and I now noticed that the material switch worked fine again.
I'm printing Ultimaker tough pla and basf BVOH (have been printing this combo for the past year).
You will see nothing special on the touchscreen display. Just the regular pause menu with turning wheel that keeps turning indicating that it's switching materials. It also indicates in the material menu that the spool in question is empty, which is correct at that point.
So, to solve the issue, downgrade to the stable firmware 👍