Temporarily losing my settings
This has happened a couple of times: I go to the website and everything is in Dutch and am asked if I want to take a placement test for German or Italian (the two languages I'm stying).
It looks like my profile has lost track of the courses I'm stying, plus my base language (English). Most settings are intact, though: I still see the people I follow.
Going to the courses page and saying that I want to learn German or Italian again unwedges things: the interface is English again and I see my progress in the skill trees.
So nothing has been permanently lost. I've seen this happen on the mobile app (Android) too where I'm presented with an empty skill tree.