I experience this for a while now, when NPCs use grenade, I take damage and being push back before that grenade reach me visually.
This is something similar to the issue with LMB in Division 1.
Here is the video, this shows the issue happened for 5 times, and in the last one, I even got killed before I react.
https://youtu.be/b-n2oHPP_pQ
This ^^^
It's been an issue for most of The Division's life cycle and to see that it's STILL an issue in the Divison 2 Beta is very concerning to me. If I had a nickel for everytime this bug got me killed in a Legendary mission in the Division 1, I'd be rich. And you know that if they don't fix this non-sense by release and release of the raid in D2, it may make the game unplayable.
THE DEVS KNOW ABOUT IT AND NEED TO FIX IT.