I recently put together a KMAC with vintage blacks. I found that my 'n' key was doing the same thing. While typing quickly I was sometimes dropping that letter. I had to desolder the switch and replace it. The new switch worked fine. After I was up and running, I took apart the switch and I couldn't see anything wrong with it. I concluded that either I had accidentally bent the contact posts while I was swapping the spring or there was just some corrosion on the contacts that was too small for me to see.
Is your board new? If so look into a replacement. If not, you could hit the classifieds for one or two red switches and try to replace it yourself.
Edit: year old. Well I dunno... Try de-dusting it?