I hate to say it but if you've adjusted the radar mount you've stuffed it. It will now need to be recalibrated by the dealership using a rather elaborate calibration unit. It's not as simple as putting it within tolerance using VCDS.I can see this is an old thread but I've recently had the same "ACC Limited Availability" warning when towing my 1800 kg MTPLM caravan with a 2019 Touareg R-Line with rear coil springs. I got the car in February after trading in a 2017 Touareg with the same suspension that I towed the same caravan with around the UK and France without any problems.
It didn't happen the first two tows but did towards the end of a trip to Ludlow where the last part of the journey was on a section of "A" road that had some fairly severe undulations which caused the car to pitch (see-saw) a fair bit.
A few days later after driving a while it reset but occurred again on the journey home via a different route avoiding the undulating road. Afterwards I researched the issue on several forums and discovered how to determine the front centre radar (behind the VW emblem) angles with VCDS to find that the vertical was +1.196 deg which was outside the +0.8/-0.8 tolerance. The radar mount has two adjusting screws, one for horizontal and one for vertical angles so I adjusted the upper by one full turn clockwise. During an 11 mile test run the ACC error reset so I again checked the vertical alignment and it had reduced to +0.451 deg which was within tolerance. I subsequently gave it another clockwise turn on the vertical adjuster which has pretty well zeroed the setting. The ACC is operating without problem but I'll be towing again shortly so will be interested to see if the problem returns.
It could be that the radar setting was close to the + limit and the effect of the caravan nose weight was enough to cause the error. My caravan nose weight is probably around 110 to 120 kg so within the VW specification for the car. I've since been trying to find a suspension upgrade option like MAD spring assisters but nothing suitable so far.
There's an update for the front camera and Front Assist systems, which addresses ACC failures. Check with your dealer if TPI 2054374/4 has been carried out on your car. It's an update in two parts, an update for the nav system and and update for the driver assist systems controler. No calibration required post update so you going to have to address that separately somehow. It's about £400 if you need to pay for it..