Yes, of course I've seen those scavs with absurd hp pool, yes, the snipers don't do a "warning shot" and go directly to the right eye while you jump and do a barrel roll. They are cracked and there's no denying it, but if they don't insta-kill you, probably it's because we ALSO are doing something wrong and could check what would we do to improve and survive next time.
This advice is for situations when you have a chance to break their line of sight. It worked for me and my 2 pals since wipe and we are playing 5-7 raids everyday, so it is not an isolated event:
First and foremost, do not underestimate them, they are dangerous, and particularly this wipe they became even harder to deal with. Whenever a scav yells at you (and doesn't insta-kill you like a freaking psycho) there is a window of aprox. 1 second until he shoots at you. If you hide behind something, they actively look for you even if you break line of sight, like every normal enemy should do…
UNLESS you crouch, conceal movement (default key is caps lock) and break line of sight for 2 seconds straight. That way the scavs turn into a skyrim NPC and forget that you are actually there, so when they see you again they scream again (with the 1-2 second window) before shooting. With that in mind, you can reposition and rush them and, with some practice, you always get the kill (they don't react well to rushers YET). Keep in mind that they'll still search for you, so another way to deal with them is wait while they try to creep on you, they make noice so you'll notice, don't worry. Of course the latter doesn't work with snipers, but they tend to prone and shoot like that. If you can get under them (like the sniper on the water plant in shoreline) you can shoot them without danger.
I sincerely hope this helps, at least until they update the scav behaviour that is making more than one ragequitting with due reasons.
I learned this form a DeadlySlob video a while ago and it's still valid.
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TL;DR: Crouch, toggle conceal movement (Caps lock) and break line of sight for 2 seconds!
