I just ran into the same issue. I got aggro'd by a normal zombie, and since I was holding a weapon I had to drop it and get out my axe. In this situation, most of the time there is no way around getting hit at least once with the zombie, since you can't move for a brief period of time. Well, normally this is no problem, but this time the zombie hit me once and I died instantly.

I was at full health, and had a hard hat on. And I'm sure that I wasn't killed by another player.

I don't think this is expected behavior as someone else said. One-hit kill zombies just wouldn't make sense with how the mechanics currently work with getting a melee weapon out.

Another thing that might be notable is that I spawned close enough to my body that I could run back. When I got back there, the zombie that killed me was standing on my body, and was bugged out such that it wouldn't see or attack me until I started punching it. Once I killed it, I could see my body there with all of the items I had when I died, but I couldn't access the inventory to loot, or check the body's pulse or anything like that. Not sure if that might indicate anything about what the bug is.