I have experienced a similar problem in the Instant Action Spring mission for A10C after upgrading to World 1.5. On the second target, I used to be able to destroy the entire squadron with a single GBU-38, but now it just knocks out a single truck, kills a couple of soldiers, and the second truck, just a few feet away drives off to take a picnic. It is as if only a hand grenade was dropped.
After posting the problem on the DCS forum, someone said that ED has plans to rework ordinance explosive effects, but as to when that happens, who knows? I wish more people would take notice and make noise to ED about it. I didn't buy this sim to just blow spitballs.