N300 (EX2700) faulty connection & device link light

My neighbor and I share wifi using extenders and the main router is located in their home. I have an N300 connected to their NETGEAR R6300v2 2.4Ghz connection and the internet connection has become very slow and unstable. At one point it worked flawlessly. Something I noticed that is very odd is the device link light. All lights are green but the device link tends to turn amber and red when I use my iPhone 6 on the extender in the same room and the connection is slow and unstable. When I connect my 2013 MacBook Pro to the extender, the device link stays green but the connection is still slow. The extender is on channel 1 while the main router is on "auto". The main router has 6 devices attached.  I've tried changing channels and updating firmware but the connection remains the same or gets worse. The main connection seems to work better when the extender is off. I've checked the NETGEAR Genie for the extender and it says everything is working properly. What could be the issue?