There are a number of things this could be:
check the slack adjusters are working correctly, there is a 12mm? nut on them turn to the right I think this should ratchet with a resistance of 13lbs ft,if it spins freely in both directions then it is u/a and the wear on the linings will not be taken up via that and the s cam. You can leaver the back of the SBA at the point it is joined to the slack adjuster and should have about .5-1" of travel.
they might not of adjusted correctly and several hard depressions of the pedal can rectify this, although adjusting with the wheel in the air and using the slack adjuster is best. Ie wheel in the air free to spin and tighten the slack adjuster until it can't rotate, then back off until it's free to rotate and there is .75-1mm of travel between the shoes and the drum, you can hear when it's ok.
Ensure the brakes are properly warm and also make sure the load sim is correct I can get all this information later tommorow. Hope this helped so far anything else let me know.