Ive got shimano race XTR m988 brakes, had them 12 months zero issues, serviced 6 months ago, no change after service.
Last 2 rides: 2/3 times per ride I grab the brake and near nothing goes to the bars…couple of pumps of the lever and it’s back perfect for another 1hr or so of heavy braking and then it happens again, any ideas??? I’ll obviously re bleed them but all I can think is the leaver seals are flipping randomly.

just sounds like they need a bleed.