Stop cooking oily food/deep frying? That certainly contributes.

It isn't so much the filters/baffles perhaps but oil vapour going up past the filter/baffle, accumulating somewhere up hood and dripping back down. Get a small step ladder, and stick your arms deep inside.

I like orange cleaner (or even Simple Green) for grease removal. Trying to make my own orange cleaner by steeping orange peel in 10% vinegar.

The hood interior and ducting, to the extent feasible, should be examined for grease buildup. Sometimes hoods are operated at a low flow rate sufficient to capture and contain modest grease generation, but not adequate for ensuring that the larger end of the grease particle spectrum is collected by the baffles. In this case grease can condense above the baffles, particularly when the ducting is exposed to cold air. Higher than minimal hood CFM is recommended in such as case -- after cleaning a far up as possible.

Could you explain why a lower flow rate results in grease landing past instead of on the baffles? What about grease traps where the vapour rises to the top of the hood and then has to travel down before pulled out by the fans?

The baffles act in the same manner as the beloved-by-some Vent-a-Hood squirrel cage blower: They extract the larger end of the grease particle spectrum by centrifugal extraction. If this is not taking place because the air speed is too low as the air follows the N-path of half of any pair of baffles, then [greasier then desired] greasy air ends up above the baffles. After centrifugal extraction, the main methods of depositing grease are impingement (due to duct turbulence) and condensation (hood and duct is colder than the plume). Slow air velocities enhance condensation and high air velocities favor impingement.

I have never investigated hoods that act as grease traps by being, it seems from your description, one giant baffle pair. Sorry but it is too late tonight to start another quest.

Not sure if it helps clarify anything. Mine is a 36” Kobe hood with 750 CFM.

Aren't those baffles dishwasher safe? I have a Kobe and I believe mine are. That might clean out what you couldn't get by hand washing.

eta: from the Kobe website:

http://www.koberangehoods.com/faq/

Also, is it possible you have some kind of leak from the outside, coming down the vent?

Is your ductwork insulated? If it’s not, you get condensation, which can carry even very fine grease particulates in the duct walls back down to the hood.