Sorry to hear. That is one of the reasons I shudder when I see vapor barriers in basements, esp w/ wooden walls. That does not mean the vb
is the culprit, but it sure is possible. The engineer is, I would think, legally liable. Call a lawyer asap and get your paperwork in order. That mess was not inspected a few months ago. Fixing that is going to be very expensive, and maybe not diy stuff to do it properly. I'd suggest you have someone with some credentials inspect it right now so you have ammo for court.