AvE's video went through what might have gone wrong, if you haven't seen it.

IIRC, AvE thought it was basically negligence by the installers. One of the mobile supports was kind of near a curb, which was going to make the bridge a pain to install. The engineers installing it decided to move the support, and moved it to a bad spot. Putting the weight of the bridge there caused a bunch of damage. The engineers should have caught it, but they went ahead anyway.