I've seen that before, on a 15 years old, but apparently unused G80 though, not a one year old Filco.
It started with one key. I opened the switch and couldn't see anything suspicious. Thought as it was broken anyway, I could as well try to learn something and poked between the contacts with a watchmaker's screwdriver to see how they worked. Much to my surprise, not only the switch survived that, but the bouncing was gone too afterwards. A couple days later another switch started bouncing, then a third, then a fourth. Same procedure fixed all of them. The keyboard worked fine after that for several weeks - until I needed the stems and springs for my G80-2100.
The only possible reason I can think of, the only thing I might have fixed by random poking in the contacts, is corrosion. But that shouldn't occur on a one year old board. Actually that shouldn't ever happen with fancy gold-plated MX contacts...
Unfortuately you can't open the switch case in a Filco without unsoldering it. If you have to unsolder it anyway, you probably better swap it for a new one. Replacement switches should be available in the UK.