Low C key not lighting

Hello everyone,

I had to part way with my Kordbot as I am moving quite far away from my current country of residence and sold it a few days ago. The person who received it told me today that the lower C key is not lighting although all lights were OK before I sent it.
Has any of you ever encountered this issue? I looked far and wide wherever I can on the Internet but no mention so far of such an issue anywhere.

Thanks in advance for any help!