bad elevation on a wet ride

I just came back from a quite wet ride and noticed that my elevation is very wrong. There are several vertical drops on the elevation map

the ride recorded just 400 over 80k 

the ride should be at least double 

where is the barometric sensor on a karoo 3? i use it with a garmin mount and the adapter is locked in place.  is it water or mud obstructing the sensor or is the karoo not waterproof!?