It looks like it was built using just wet sand. But there's a (slim) chance it's fine now, and the damage occurred before it got chance to set.
Is there a water source? E.g. is it holding back soil or is there a downpipe? It's possible that it was just that some of the bricks were very wet when it was built, and the water oozed out of them. Or it was left half-built then the holes in the bricks filled with rain, which got squeezed out when it was carried on later.
Can you dig out the mortar with a screwdriver? If so it needs taking down and rebuilding, this time using some cement. If the rest is firm then perhaps it just needs a tidy-up with a brush and some brick acid and a repoint.