router loosing connection until it is flashed

hope I got the right forum!

I have 2 xbee s2c modules, when they have the same pan id they connect ok.
but if I change the pan id on the coordinator they no longer pair up (which is ok!)

my problem is that when i change the pan id back in the coordinator it will no longer pair up to the router, in fact … after this happens the router acts buggy , it no longer responds on the pan, and even struggles connecting to serial on xctu (i need to hit reset on the module every time i read/write with xctu on serial) … this problem goes on until flash the device firmware and reprogram it … then it starts to pair with the coordinator again… and work properly on serial again too…

can someone tell me why this happens!!>>???
can someone tell me why this happens!!>>???