Recent 12,000 service, which includes forks. It almost seems that there are air pockets in the forks which create a bit of a smacking noise on rapid bumps.
I can grab the front of the bike and bounce it real quick to recreate the noise. Are air pockets capable of this phenomenon?
Make sure the fender is not hitting the fork tube. Other than that... ???
My knowledge is limited on the mystery that is Front forks, but it sounds like Cavitation.
I won't pretend to know how to fix it (Oil height a little low?)
But I would suggest take straight back to where the work was done and speak to them, or speak to a suspension specialist.
Since I can't hear the noise I can't say, and probably couldn't even if I did, but CairnsDuc has the right answer.