time capsule disconnecting from certain devices

I need some help figuring this one out, My time capsule is disconnecting from my Nest thermostat, My roku and my Tivo box....It has largely been fine for the past year but now it just disconnects and then the devices wont see the wireless network anymore. I reset my time capsule and all is fine for about a day but then the same thing happens again...What is really strange is that my ipad, imac, galaxy tab and other devices work fine...the issue seems to be limited to the three devices mentioned above. One thing to note is that I allow my neighbor to connect to my wifi and give him my password...I dont know what he could possibly be doing that would effect what I have described but I did notice that the problem happened again after I reset everything and gave him the password...Thinking of resetting again and creating him a guest network and see if that makes a difference...any advise or similar experiences would be of great help...I gotta get this one solved!

 

just a thought, but what are the odds of something being wrong with the 2.4 ghz band and the devices in question can only connect to that band...I know the nest only works with the 2.4 not sure about the other devices...