Mikrotik RB450G not response after one device connected

I used Mikrotik RB450G, when I installed the POS (EDC) terminal to Mikrotik RB450G (OS 4.14). When doing ping test to Mikrotik, Mikrotik did not give respone (RTO), but if I release POS Terminal, Mikrotik will give respone. What caused that to happen?..

Gunawan, Jakarta - Indonesia.