I've played around with the settings and I've yet to encounter anything I would describe as "hard jerking" - only some very slight jerking at center. This I believe is due to the G29 emulation in GT Sport - the G29 has a natural deadzone and the Fanatec doesn't. They need to add in a deadzone setting like on my old 911 GT3 wheel. But as I said, that jerking is very slight - more an occasional, minor nuisance than anything that will affect my driving experience. Fei seems like the most likely culprit to me, but I've played with that and whilst it definitely is less smooth at 100 than 0, I still didn't get anything more than mild jerkiness. I settled on 40 for it.
Are you using the clamp or are you hard mounted? And also, is this only happening in GT Sport or any other games? What car are you using?
Also, I've listed my settings for GT Sport below. I'd recommend trying the exact same setup and seeing if you still get it. The same wheel in the same game with the same settings should equal the same experience, so if not then it seems to me that you have a defective product and should contact Fanatec support for a replacement. Also for the sake of keeping as much the same as possible, some of the cars I've used are the BMW M6 Gr3 (the one I tested this most extensively on), Ferrari 458 Gr3 and Gr4, Corvette Gr4 and N500, Mustang N400 and Toyota FT1 VGT Gr3. Maybe try one of those cars.
Here are the settings I've settled on:
Sen: Aut
FF: 080
Sho: 100
ABS: 100
Dri: -05
For: 100
Spr: 100
Dpr: 100
Fei: 040