I see this all the time. I'm sure in some cases it is decync from internet lag however what appears to happen is combat isn't initiated until you swing. Then the mob turns and hits you. It almost appears like a combat trigger. So I never get the first hit in even if I run full speed up behind a mob smack him in the back. That should be a big hit but nothing. This takes away the advantage of getting the first swing in (especially a back attack).
And I agree with River on this,
This whole migration thing seems like a complete over kill in my opinion. What I would have liked to see is to simply create a low level zone around the lake and keep the animals there at a level that new players can handle with a bit of overlap (There needs to be an occasional scare to keep things exciting). The rest of the world should be as natural as possible. There should be small young animals, medium animals and large very dangerous mutant animals. Just how it was around 3 or so months back. If the animals had not been wiped out at that time it was a great system for all experience levels. Sadly a few people chose to clear the map, then demand everything change and this is what we have now.
And lastly I thought the zone information was just for the test server. I was surprised to see it in game. I think it totally takes away from the realism and is honestly just annoying. All anyone needs to do is to go out and explore a bit. If you see scary creatures then run away and head back toward the lake. But a revenant count? I really see no purpose in this at all.