Airplay comes and goes with ios9

I have an iPad 3 running the up to date version of iOS9. My wifi is used with a TP-link x 2 extender through the electrical circuits of my house. I also have Apple TV4 linked to wifi via one of the TP-link extenders. When I try to use AirPlay from my iPad to TV, the Airplay does not show in the control centre. This morning, having not switched on Apple TV, Airplay is showing, and is showing on my iMac (which sits next to the router and is connected by cable). As requested on various websites I have checked the wifi networks and find that the last 2 numbers of the IP address is different on the iPad and the AppleTV. Does this matter? And is this the problem? And how do I sort it out?

I have tried switching off and on the wifi on the iPad while standing next to the TV but the IP address stays the same. I recently had to reset up all my wifi and email after updating my iMac to El Capitan.

Broadband supplied by Plusnet. I didn't know whether to contact Apple of Plusnet first.