climbpro freeride reported gradient

Had my 840 since June, used in the UK and it seemed ok most of the time but there were some times I was questioning the gradient shown on screen, but wasn't sure if it was faulty or not, i.e. is this climb really a 6%, feels a bit steeper...?

I've just been on holiday to Tenerife and when using climbpro freeride the little moving flag that appears over the climb profile and also shows the current gradient was constantly wrong. I was sometimes on a "canarian flat" .ie 5-6% and it would show 0 or 1%, and whilst ascending the Masca climb on one of the steepest ramps which felt like it was nearly 20% it was showing only 2%

this seems to be just with the freeride, when I have a rote loaded it's much more accurate, but I do think it lags sometimes and as I get to a steep part it's still showing me a lesser gradient for 10 secs or so