I'm willing to bet you are dealing with Wi-Fi interference from a neighboring Verizon customer. The fact that the problem has come and gone in the past and worked between 3 and 6 today hints that the neighbor may have been off line during the times the problem wasn't evident.
I am more sure than ever you need to get a Verizon tech out there to sort this out. I remember you saying the landlord had to give a Verizon tech access to a closet. Your problem may have started then.