Mac – Apple devices keep dropping off wifi

I have been having an incredibly hard-to-diagnose home networking problem for the last month. It’s not easy to summarize but I’ll try a TL;DR: I’ve had a wifi network that worked perfectly for over a year. Starting a month ago, every Apple device in my household will repeatedly drop off the wifi network. But a Windows PC that a network tech brought over is able to stay connected to it. This happens with two brands of wifi router, and with most but not all SSIDs we broadcast on those routers. (!?)

My main questions are:

• Can Macs and iPhones have problems connecting to wifi networks where Windows devices are fine? And even where those same Macs and iPhones worked perfectly on the same network for a year?
• If so, is there a way to fix that?
• What else could cause the wifi issues described in detail below, and how can it be fixed?

Timeline and details

AT&T is my ISP. I’m on a 45MBit plan with copper twisted pair lines to my home. For a little over a year, I had an eero mesh network of 3 devices. The AT&T modem (made by 2Wire) was the entry point to the house, but I turned off its SSID. The eero routers were providing wifi to the house. For 13 months it worked perfectly.

Then in mid-May everything went to hell. On May 18th at 11am, devices started dropping off the wifi. It happens most often in our family room, even when sitting still, 3 feet from one of the mesh routers. It happened on all our Mac laptops and iPhones. (3 Mac laptops, 1 iMac, 4 iPhones, all of varying ages.) I also have a guest staying in our backyard cottage, who has a Mac and an iPad. She is reporting the same problems.

One neighbor started having similar problems within half an hour of the same time, even though he's on Comcast. The neighbor in between us installed a new Cisco Meraki router that same day. (Could it cause interference? I asked him to disable it for ten minutes as an experiment, but that didn’t fix our problems.)

I spoke to Eero support and AT&T support numerous times. Here are some relevant details and things I’ve tried:

• If I Option+Click the WiFi icon in the Mac menu bar when sitting in the family room to show debug info, I can see the BSSID change to 00:00:00:00:00 right at the moment my connection drops. It’s easily reproducible: just sit in this room for a few seconds to a minute.
• I made sure my eero mesh routers are not placed too close together to be overlapping. Eero support confirmed this for me.
• Sometimes it shows two copies of my network in the WiFi menu. (Could this be due to having a mesh?)
• When I run WiFi Explorer, it shows occasional drops to zero signal for all my eero devices.
• When I enable wifi on the AT&T modem/router combo and attach Apple devices to it directly, they don’t drop off. (But it doesn’t have enough reach for the whole house and cottage.)
• I’ve run multi-hour ping tests while directly connected via Ethernet to the modem/router combo. The early results were bad: 1.6% packets dropped. But AT&T made some remote fix, and the most recent test has 0.0% packets dropped.
• Eero support said they were noticing some strange drops in the incoming service to their device. But an AT&T tech said my home’s connection to their hub is exceptionally good, with no glitches at all.
• AT&T replaced my modem/router combo for good measure, but the problems persisted.
• AT&T did a board swap at their hub. It still didn’t fix the problem.
• I hired a local network tech and asked him to set up a new system for me. He did: two Ubiquiti access points and a Ubiquiti mesh point out in the cottage. He first set up an SSID called myNetworkTest and one called myNetworkGuest. Once he got them working he said ok, now let's create your main and guest networks with the names and passwords you want, and we’ll delete the test networks. So we set them up. BUT:
  • All Apple devices in the house can connect and stay connected to myNetworkTest with no problem. But for all other networks set up on the same hardware, the Apple devices accept the password but then they just keep trying unsuccessfully to connect.
  • His Windows laptop has no problem. It is able to connect and doesn’t drop from any of the networks on the Ubiquiti hardware.
• I’ve tried disabling Bluetooth on the Apple devices, in case they are using that to communicate with each other about some network being bad.
• I’ve tried deleting the plist files on my Macs so they forget their old settings
• I’ve tried creating a new Network Location in System Preferences.
• I’ve tried resetting the SMC and PRAM.

I’m just at a loss, and so is the network guy I hired. Neither of us has ever seen anything like this. He could rename myNetworkTest to the name I want, but we don’t even know if it will work or make things irreparably worse. Or I could just use the network using that name, since the name doesn’t matter so much. But then I wouldn’t have a guest network, which is important to me because I have guests who stay in the backyard cottage.