I agree…took me literally months to get them to actually acknowledge a significant firmware bug and do something about it, and that only happened after airing it on their forum. Might be worth a shot there?
Never had Linksys or Netgear so I cant speak for them.Have had Asus and have had great customer service from them.
I see you have a couple of UBIQUITI UniFi UAP-AC-M AC Mesh Dual-Band access points.How reliable are these ? Have one area of my house were wi-fi drops off wondering if one of theses would work.
Ive had one unify AP (AP AC Pro) fail at a clients after a couple of years…but otherwise very reliable. Maybe a tad of a challenge to setup as you need a controller program to do so but it can run without that being there once setup. Plenty of how to’s on youtube can search willie howe or crosstalk solutions.
Note that I run all mine wired not meshed.
My house is hopeless as its older construction appartments with lots of concrete and rebar and 2 storey, inside walls and floors are also concrete and brick so essentially I have an AP in every room (2) and a couple more to cover the bigger area that has a u shape part where the signal drops off in the kitchen. I also remotely run another single unit at my inlaws place with the same SSID so that when we go there or they come here no need to swap networks 
plus I have a unit setup for when I travel that I can just plug in to any lan port and it will boot up and be just like home for me anywhere I am…
BUT I do this stuff for a living too…so my house is as much a LAB for me as it is my home network.