Comparing blocks.xml, a17b240(1st stable) & a19b178 (can't find a18.4 files atm) there doesn't appear to be any changes in the Damage bits.
Still 20 dealt for 4 taken, and max of 2000, break percentages the same.
Might be that zeds are targeting the center of blade traps more than previously? I know from trying various designs in previous alphas that if you can keep the central hub of the blade traps out of the zs path they rarely hit it, and that made a noticible difference in the damage taken.
Oh, and if by chance you were using a half-block height design before and aren't now, then the central hub may be seen as an obstruction, so zs are trying to break it.