Help Max HD2

I am using Peplink Max HD2. The network structure is as follows; I have a separate router that manages the local network system. It is connected from the LAN port of the Peplink modem to the WAN port of the Router. But peplink locks the whole network system when there is no internet in the modem. I can’t connect to any device via wifi. When I remove the cable from the LAN port of the Peplink modem, the system returns to normal. I tried by making the main router peplink modem in the system. I discovered that the modem does not give IP to the devices when there is no internet. Does anyone have any ideas or solutions for this?

This sounds really weird. When its working, what IP address does your separate router get on its WAN from the HD2?