Hi,
I own many Arturia controllers and that's the first time I see an issue like that, though I remember that there was a similar issue with KL88's MIDI DIN out only (not on USB out) but on random keys (it was an early firmware issue).
In your case, it seems like it's something specific to that key i.e. hardware issue, so I suspect that unit needs to be replaced.
You need to contact Arturia's Support:
https://www.arturia.com/support/askforhelp/issuesMaybe contacting the store where you bought it might make the replacement faster, not sure.