The bouncing tanks go over other objects with #85 matId just fine, with no bounce. Just not this one bridge...

I've looked at some of the tanks that bounce, to make sure their col01 and col02 weren't too close to the ground (ground clearance), but this doesn't seem to be the case. I'm at a loss right now as to what could be the issue.
Does anyone have any ideas? Things to try? Anything???
tia, takiwa