This is yet another example of how unsafe it is to write arbitrary stuff in the entvars when the engine doesn't expect it.
By setting this, you are overwriting what the engine already writes at the same location. The question is whether you write it before the engine passed here or after it.
And there's also a problem with the clients. All your clients' DLL (including your listen server client) are programmed to know that when a player respawns, his health starts at 100. You change this by the engine side. But then, all the clients' predictions get out of sync. If you make a change to a player's health arbitrarily, send an update network message to all your clients.