They key-mechanism is also different from 'normal' keys, see this:

Rather unusual is the metal clamp that goes from the key cap through two openings L and R of the key mechanism.
Does anybody know why that clamp is here, and/or what it does?
Sometimes the Fn-key functions correctly, including switching on/off the KB backlight via Fn-spacebar.
Other times it does nothing.
I can't see any dirt or broken/missing parts, can you?
This behavior is apparently not uncommon with the X240 and has been a thorn in people's eye for many years.
This Fn-malfunctioning can happen from buying new, from swapping the keyboard, but most likely (I guess), from updating the BIOS.
And of course, since UEFI you no longer can revert to older BIOS-versions, unless you go through great hoops!
As usual, Lenono doesn't give a hoot and has never tried to rectify this!

Does anybody have any explanation why this might happen?