try this… Legend O= Player One 0=Player 2 G=Player 3
this was my issue
Player one shoots line trace on client.
G O----------0
Player one shoots line trace fully replicated
this is player ones screen
G O----------0
However this is players 2 and 3s screen
G----------O 0
therefore player one has just killed both players 2 and 3 without even knowing how he killed player 3 lol
Easy fix, do not replicate your line traces, replicate your Hit condition and Hit results FROM your line traces 
(works well even with damage system)
now it looks like this
Player Ones Screen
G O--------0
Everyone elses Screen
G O 0
But everytime the line trace on Player ones screen hits something, thats when you are golden with replication and gets rid of all line trace calculation functionality issues replicated to the server, it just applys the damage, plays the effect, and spawns a bullethole decal wherever player ones line hits ;D