Ok - I have found a solution to the issue - apparently if you have Project CARS 2 installed, and (I think) you use custom FFB files, it alters some registry values which cause this issue in F1 2018.
What I tried first: (none of these helped)
Uninstalling and reinstalling Logitech Gaming Software (on latest version), reboots in between.
Verifying game files via Steam
Resetting all control defaults in F1 2018
What did work was this:
Go to HKEY_CURRENT_USER\System\CurrentControlSet\Control\MediaProperties\PrivateProperties\Joystick\OEM\VID_046D&PID_C24F
Check these values, and change if required - it works for me:
OEMName: "Logitech G29 Driving Force Racing Wheel USB" must be instead of "G29 Driving Force Racing Wheel"
OEMData: 43 00 08 10 19 00 00 00 must be instead of 00 00 00 10 00 00 00 00 (or any other value)
Reboot your PC, and the FFB wil be back for G29 in F1 2018.
I'm still getting a bit of clipping so would really appreciate some of you posting your G29 settings here for F1 2018, both Logitech Gaming Software and in-game settings.
All the best, Merry Xmas to all