Enemies do not fall when floor is grenaded out from under them.
It would be better to take a screenshot and post it along with F12 functionality. Because for me enemies always fall down. Maybe you have discovered some specific place where it doesn’t work.
This occasionally happens to me, they do fall eventually but it can sometimes be very slow, up to a minute to happen.
And before anyone asks…8600k oc’ed to 4.8Ghz and a EVGA 1080Ti SC2 currently without an overclock.