HI everybodyI am trying to collect info and oppinions and suggestions on this subject.
We are a group of enthousiasts with different xj`s.
2003 xj8 4.2 na LHD 359000km x350 seems to have second set of bilstein B4supercomfy generally . after highwater on the left side in the winter go all 4 heightsensors changed wich feels like a guessed improvement of 10-15%.
2003 xj8 4.2 na LHD 214000km x350 with a set of second hand bilstein after we had Miessler airsuspension installed ( what a disaster super stiff , no improvement no fun)
a 2007 DAIMLER lhd super eight long with just180000km exellent comfort so far and a real powerhouse x356

and then a 2007 x358tdvi with bilstein B4 second Hand and really struggeling with randomly jumping in transport mode. Stays soft for 2days then maybe after restart stays soft or either hard
just 2 days ago we put brant new original heightsensors on the three corners. Aftera first drive wow what an improvement super soft ride, even with old airstruts.
next day after approx 30km and 3 stops with engine off just before a longer distance ahead, jumped back into super stiff mode

SO, if somebody knows a little more about this frustating problem we would be glad to get into discussions

 

You will be aware that the control module is behind the rear seat ?
Disconnect battery and unplug control module clean pins and look
for bad connections etc.
Search this forum for pics etc about how to dismantle rear seats.
Above is just an educated guess but worth doing?

 

Do you have the possibility to read codes? If there is a problem with the control module, you could well have an error code shown for that.

Apart from this, +1 to Meirion's suggestion.

Best regards,

Thomas