No brakes

Whilst driving a 12T rigid with air brakes I was approaching a junction and I had almost no brakes at all, the truck was stuttering under braking as if the ABS was working. The air pressure was down but quickly recovered, no sign of leaks and it was fine until this 1 incident. Now I’m worried that this will happen again and next time I could be laden and travelling at alot more than 15mph. Truck has been defected but if they don’t find anything i’m going to be stressed when taking it out.

Opinions please on what you would do in this situation?

How much load on the front axle?

The truck obviously needs a good check over,but remember that the brakes are on until the air pressure builds up and releases them.

Truck empty so front axle weight was minimal.

Could be something other than air then yes

I am thinking it could be a cracked brake disc or you have lost a brake shoe.

Had you just tipped the load somewhere beforehand?

Multidrop so gradually losing the load throughout the morning.

This happens more than you would think.Happened to me about 4 times.
First couple of times on Mercedes actros.First time going down the M58 red BS fault flagged up on the dash when I was doing about 50 mph.
Touched the brake pedal and nothing.Lucky not much traffic about so got onto hard shoulder and stopped with handbrake.Turned off ignition and fault had disappeared.When I got back to garage put truck on stars but no fault was logged.

Have spoken to a few drivers who have had this happen but of course the manufacturers say its impossible.I think the problem is that the EBS system which is the primary operating system somehow goes offline.The problem is that if the EBS shuts down the default pneumatic system doesnt seem to kick in and your left with no brakes.
Also happened on a Scania bus but was on the brake tester.Pedal to the floor but was pulling less than 500 kg on both front brakes.Same again turned off ignition and EBS reset itself and no fault logged.Bloody frightening when it happens and if you ploughed into something and survived nobody would believe you.

Pinhole in a brake diaphragm?

Sounds like a diesel spill on the road TBH.