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.
Refer to previous link I sent you(as well)...but the channels should be 1,6, 11. Sometimes..even though those channels do not overlap....you could have heavy traffic on a channel next to either 1.6,11 ... and that could slow down your speed/cause disruptions.
You may feel more comfortable calling Verizon...and that link me be outdated...but that is how you do it. I am assuming your wireless network is secure and not open...correct?
Verizon should be able to clarify what the issue is...just make sure to tell them when you ran your diagnostics it said "congested traffic"(specific wording only)....and you can also mention the other information you gathered from the diagnostics.
Someone may have a weekend pain in the ass guest/or someone being malicious(doubt that strongly)...or it's on verizon's end....
Many times...carriers will upgrade/do maintenance over the weekend as well.
!!If your router is next to your desktop...just plug in the Ethernet cable...and all should be fine. I have 50' cables in my shed...but I'm a little too far away...eh?
Call verizon if you are concerned that you can't do it yourself....they can test/change on their end
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