He ran a better 40 than expected though, so I didn't think that was going to be an issue. Maybe his separation just wasn't there on tape? I just don't get it.
I don't have any insider info, but when teams have suspicions about a player's speed I wonder if a better than expected 40 time does much to sway their opinion. Lazard spent the better part of three months training almost exclusively for the combine tests, right? So just because he was a tick faster than expected all that really tells teams is that he put the work in on his sprint drills. It doesn't necessarily make him a better football player or faster in pads next fall.
I think it may have been a combination of things against him - like you said, a lack of separation on tape, a history of drops, he's kind of a tweener, and the fact that he maybe doesn't offer a lot of versatility as a special teams contributor.
Even with that taken into consideration, I was surprised at some of the names called instead of his on Day 2 and 3. I think he'll make it in the NFL just becasue of his sheer size and jump ball ability. He's a red zone threat for the team that figures out how to deploy him.