It seems that either the multiple tech bug/exploit is back in some way or someone is just cheating via external means.
The following pictures show a ranked 4v4 that happened not long ago and one payer (P8 Genki) is able to get WheelBarrow, Bloodlines, Forging, Siege Engineers and Double Crossbow multiple times.
Ballista.aoe2record (4.2 MB)