Current Settings:

Phone [A] static IP: 192.168.1.8

Phone [B] static IP: 192.168.1.9

Router:

            RULE_A: forward(19100-65535) ports to 192.168.1.8

            RULE_B: forward(19100-65535) ports to 192.168.1.9

When Phone [A] runs as Server, have to change Router Settings:

1. RULE_A : ACTIVE
2. RULE_B : DEACTIVE

When Phone [B] runs as Server,have to change Router Settings:

1. RULE_A : DEACTIVE
2. RULE_B : ACTIVE

observed result

whenever Phone [A] or Phone [B] wants to play as Server have to change Router Settings or at least check if his RULE is active.

NOTE: 

I could included this issue to MCPE-109286 ,but 

here[ 1 ticket = 1 issue ]