I guess you have not changed default destination addressing on Coordinator.
By default, Coordinator sends data on broadcast address 0xFFFF. Change “DH” and “DL” parameter on Coordinator to match it with “SH” and “SL” of Router respectively. This should solve your issue in my opinion.
If you only have a few routers, then using API mode and Unicast addressing would be well worth it. You could then send the data to each node faster than using the broadcast address. However, if you have more than 40 or so, it may not be worth switching to Unicast and API mode as the rout discovery may star to be too much.