At KFC, there were lots of failed LED filament lamps, where the filaments glowing only at the ends, much like a preheat fluorescent with a stuck starter.
What can cause this?
Interesting! Never seen anything like this. Common failures are filament pair off or flashing, possibly also dim glow of all filaments. Maybe the central part of the filament got short circuited and only ends survived thanks to better heat dissipation?