This actually happened on 7th December 2024. I bought Fiio FT1 a few weeks earlier and was using them from time to time, enjoying their bass, switching between other headphones. One night, when I was trying to put them on my head, they suddenly disassembled by themselves. After a little shock, when I managed to understand what just happened, I began to look around for parts. I found these 3 small elements, which look like a torx screw, a socket and a gasket.

I though that maybe I'll be able to fix them myself, but firstly I would need proper tools. Secondly, I found a video how they were assembled and they used an additional gasket (4th element), which was semi-transparent and plastic, to insert between two metal parts of the chassis - which I haven't found. I already contacted the shop where I bought it.