Same problem here, albeit with tier0_s64.dll on dedicated servers.
Happening since I activated the Steam plugin on 4.16
Edit: This post seems to have the answer → C++ 4.16 Transition Guide - C++ Programming - Unreal Engine Forums
I am trying to learn how to build a dedicated server for UE4. I’ve built the 4.16 from source, and have subsequently compiled a dedicated server binary. However, when I launch the server, I am presented with the following error.
The procedure entry point Plat_CommandLineParamExists could not be located in the dynamic link library C:\Program Files (x86)\Steam\steamclient64.dll
I looked in the source for the compiled version of the engine, and in the steamworks sdk folder, there is no steamclient64.dll for me to overwrite my local copy with. I have downloaded several recent versions of the steamworks sdk as well, and none of them contain a steamclient64.dll
I’m not really sure what the root cause of the issue is beyond some type of version incompatibility. How do I fix this issue?
Same problem here. 
Maybe you had to put this in Bug Reports, so that the Epic Staff can see it.