Socks can get caught in the rubber seal between the door and the drum. When washed, they are then drawn inside the machine where they get caught on the heating coil.
The heat and friction will cause them to gradually dissolve. To prevent socks from disappearing in the washing machine, there are a few simple solutions. Use a laundry net or sock clips. Alternatively, a household rubber band that you can use to tie the socks together in pairs can also help. At the right washing temperature, socks become hygienically clean again.