Powerline XAVN2001 drops off network

 Your problem could be with

• the extender->router ethernet connection
• the extender->extender powerline connection
• the extender->client wifi connection

It'd be helpful to figure out which of those is failing. 

I suggest that next time it happens you should try powercycling the extenders (and not the router), and see if that is enough.

If that also works, then the time after that try powercycling only the ethernet-only extender at the router, and see if that is enough.

Then try the wifi extender module.

That will hopefully give us some clues on where the connection is failing.