Can't change channel in X-CTU

I always have a problem with channels. When I set the same Pan ID to xbee modules, they may have different channels. Then change module from coordinator to router, after that they find same channel and work. But after several time they stop working and when I check they have another channels. So, why does this happen???
PS:Sorry for my english) and thanks!

are you referring to the CH value? If so, that can’t be changed. It’s readable only.

To control the channel used you use the SC value:

If you have a secured network, and if you don’t want to loose the modules after power cycle, you can set JV=0 so that the module retain its parent and search for the parent in the specified PAN ID after power ON.
In your case as said, CH value cannot be changed. It is Read-Only parameter.
You can issue NR0 to reset the networking parameters. Or write the firmware again with default settings.