ARR calculation
Come up with a solution so that, even if one of the racing categories is Carbon, a rider is given an ARR rating.
As example, my ARR defaults to 200 at present as I am Carbon in climbing, however if my other 3 ratings are added together and divided by 4, my potential ARR would be around 650. That seems a fair way to categorise me as 200 is too low

Many thanks for your suggestion and support for TrainingPeaks Virtual.
This is working as intended - your ARR is your all-rounder ranking (literally A.R.R.) and therefore reflective of your abilities across all types of riding. If you don't do many climbing events, and therefore there's no climbing data for TPV to accurately categorise your climbing ability, then it also can't calculate your ARR.
If you do another couple of climbing events, then you will get an ARR....but if you're not an all rounder, then you won't have an all-rounder ranking!