Power lines PL1000 dro out when I add 3rd router to my network

Ok so my my current network is two bt smart hub routers connected to each other via an Ethernet cable and then I have two netgear pl1000 that feed from the main router.

I want to add a third bt smart hub router to the system, I connected the third router to my second router and everything router wise was working perfectly. But I turned my tv on (connected via the pl1000 and it had lost connection. I checked my other tv also connected to a different pl1000 and that was down aswell. If I unplug the Ethernet cable that connect the third router the pl1000’s both start working again.

Can anyone help me fix this issue?