Try low server performance servers
OR/AND
Have a ping above 150, and connect to these servers and try

-Alert and Aggro the zombie
-Then start to block, and go backwards

Other issues:
Sometimes Infected are spawned in by the server, stuck on some sort of structure or geometry, not allowing them to move or go to attack you

Infected are teleporting at times to you, especially when they're aggro/alerted on you, and are stuck on geometry like the above ^

Infected can still go through walls and doors at times :/

Infected are super super slow, or can't even get into buildings/door entrances at times. (making hiding in buildings super easy, unless they walk through the wall)

Sometimes in melee, when fighting infected you can go inside of them while punching them if they move into you (running attacks, etc.)
ruining the flow of combat w/ them.