I currently have a 2017 evo and brakes are fine....apart from when used in deep/thick mud. Under normal riding I ride with one finger on the brake, then after the mud the lever will pull easily to the knuckles of my fingers and I have to shift to a full grip with little effect, very off putting, just like if they had air and needed bleeding. This effect will then slowly wear off over subsequent sections. After trial and bike prepped everything back to normal. Removing the caliper shows a big build up of ****/mud. I'm favouring the removal of the pad shield at the top of the pads/caliper as a possible solution ??????

Anybody anything similar and a solution?

The throw of the lever shouldn't be affected though the necessary braking force will increase. Make sure your lever adjust allows the master cylinder to uncover the reservoir port at rest so the system pressure can normalize. Typically this causes the brakes to overheat and grab but if the mud is cool it could have the opposite effect. It's also possible for mud to pack in the pads so they get pushed out screwing up the self adjust nature of the brakes. I've wondered if this was going to an issue with the new FIM "solid" rotors.

During the event you can drag your brakes on the loop and get some back after a water crossing.