Listen server recommended number of players?

How many players should 1 listen server have to have smooth movement and everything replicated without problems ? Currently my project has max 10 players and when trying packaged version and opening it 10 times on my desktop i have some problems that i don’t see when i try it with 3-4 players. Is it due to me opening 10 projects on the same machine or would it be different if i test it with 10 computers( 10 different steam accounts) ?

You need to test it yourself as there too many factors, including specs of server and connection. Ofcorse running 10 instances of game will not give you proper realistic measure and ofcorse best solution is to test it on 10 different computers. At least run server on different computer and try to connect it 10 playes to it from single machine from other computer and look on numbers in server, but even so lag of running 10 instances of game may effect server performance.