Two years ago I had a similar problem with my new Fox (36) Forks.
Funnily enough they were fine around Llandegla when I went for a test ride, but when I got them out to the Alps I was getting absolutely battered. I tried everything to get them working properly, but just couldn’t. On the plus side it was worse if I was on the brakes, so I stopped braking.
Then, prior to my next Alps trip, I got them serviced, they removed loads of grease from the lowers, and they were brilliant.
Fox 38 are meant to be even better. I suspect you may have a similar problem to the one I had with mine?