We do occasionally see ‘crossers coming in for workshop work. Usually the owners do loads of the mechanical work themselves- it’s the only way to keep it affordable- crossers need weekly attention- at least a wash and drive train lube after being hammered around a muddy circuit.
Just about all crossers have front braking problems initially- either they don’t stop or they squeal and judder- hardly confidence inspiring when giving it 10/10ths in a race! Light canti’s tend to be flexy and non-adjustable, so getting a better set of Shimano or Tektro canti’s is a good start.
Judder is usually caused by the long free cable runs- for example the long run from below the top headset cup to the straddle cable- this run varies in length substantially as the fork deflects under braking. What happens in slow-mo is that the fork straightens under braking which tightens the cable, applying the brakes harder which straightens the fork more etc until the front wheel briefly loses traction, then the fork springs back and the cable loosens- this is probably the root of the judder on flexy forks and long cable run bikes.
Working out how to fix this can be expensive (new fork) or cheapish – if you can figure out how to shorten the cable run- on smaller bikes a long cable hanger may be enough, or the Tektro hanger (installed on the calliper brake mounting hole in the crown of the fork) can work a treat.