With 'bad' aluminum my first suspicion is wrong temper. What was the chip formation like; similar to old stuff or are the chips stringier? It is not easy to tell if you are milling it but drilling holes or turning low temper aluminum can make long stringy chips. The higher elongation number suggests lower temper material that is more ductile.
Have you got back to your supplier to find out if this is sourced from the same mill as your earlier orders.
An open mind is a virtue...so long as all the common sense has not leaked out.