How to read several Modbus commands and respond

My setup is as follows:
An rs485 device sends a request to a xbee coordinator that sends it to a router and this one to another rs485 device.
My problem arises when the device linked to the coordinator sends requests faster then 1/second. Sometimes it sends the request but is unable the get the answer. So there isn’t like a request/response sequince, sometimes it sends 3 requests and then gets 3 consecutive answers.
This is only if the coordinator is in broadcast mode, but i need it to be this way because i want to use 5 routers.

Update: I have set up a point to point connection: coordinator to router. Now the speed is almost good but i still send 2 packets before receiving the first one. I mention that the rs485 device send it’s request at about 48ms. Still isn’t solved.