EX6200 EXTENDER KEEPS DISCONNECTING FROM THE ROUTER

I have had the EX6200 extender for a few years and it has worked fine up until about 6 months ago.  It keeps disconnecting from the router or just loosing internet.  The light stays Green showing connection but my internet keeps going in and out.  There has been no change in the discance between the two and no obstructions.  It is in another building about 300 feet away but has worked fine at about 40% signel strength from the router.  I have to turn the power off to get a connection and sometimes have to do a hard reset and go through the set up process again.  It will work for a while then start to loose connection again.  I had the router from my DSL service replaced and that did not correct the situation.  I have low DSL connection here anyway with no way to get better internet or DSL.  It is very frustrating that the internet keeps going in and out all the time.  Where the router is connected to the DSL that seem to stay connected ok.  Just a problem with the extender has just popped up.  need suggestions.