After check site condition, find the two power supply to PNPN coupler only one is switch on.

The error not happen again until now. 

For problem happened in this project, Could be the possibility that only one power supply to PNPN coupler, can cause PNPN coupler not work stable. 

Hope this information can help other engineer. And it also remind me to check PNPN coupler power supple in future project..