Simulation is done and the good news is that it runs correctly and your problem is solved finally. The reason for the BER=1 in one of the channels is the symbol rotation problem. So if you put laser initial phase in the receiver of the user with bad BER equal to 110 in this case, you will have no error. Another thing you must pay attention to is the value of amplifiers in the line, which should correspond to the loss of the line.