Two week long saga - Devices coming and going with xFI and issues with 3rd party modems and routers

I think this is day 14.  For about two years I have a modem (Arris S33) and router (TP-Link Deco X60 Mesh) that worked fine.  Then problems started first with some light switches not connecting and (if I remember) some Echo boxes going offline for a while.

Then I got an xFi box (can't remember model)from the local store to work around things while I got what I thought I needed - a replacement modem.  I had problems with the xFi box - some devices would connect - others would not, and this list would change over time.  The management screen (10.0.0.1) and the app never seemed to agree on the connected devices.  Two wired devices, Tablo boxes (these are like Tivos but are accessed via apps on Roku, etc.) have NEVER connected since the problems started.  The problems do not seem to be device specific since I've had issues with Amazon Echos, TP-Link light switches, Roku boxes, my solar system controller, etc.

I have tried other Modem/Router pairs.  The one that comes closest to "working" is Hitron Hoka56 and Asus XT8 mesh.  No devices actually connect to the internet but I can see that the Modem is getting an IP and DNS info and it look like all devices attach to the Asus BUT nothing gets through.

I've had over a half a dozen calls including a call-back from advanced support. Except for the support person who upgraded my speed without asking by "bundling it" with a request to have a service person come, everyone has been professional. (I'll downgrade the speed and fight the charges later.)  The advanced support person put in a request that I be allowed to swap the xFi.  I did that and no difference.  A person came to the house but is pretty much limited to checking the lines and hardware.  They're all fine.

Th service person said the only thing he has seen that when all else fails, essentially resetting the account.  The way he described it, the old account is wiped clean and then "rebuilt" or even the old is eliminated and a new created.  The person on the phone when I called after that thought either he or I was crazy.

Another odd symptom is that when I use my phone on wifi, occasionally unusual things happen.  An example is that I get a news related email showing the start of a number of stories.  When I click on a line I get an unusual error message.  If I just turn off wifi on my phone, it is just fine.  I've seen times when other apps act differently when used via wifi vs my cell carrier.

My frustration is through the roof.  Not only has this been going on for two weeks but dealing with the phone tree and dropped calls has made it worse.

Even though they have different symptoms, I'm convinced that the xFI issues and the routers not getting through the modems are related.

Any ideas?

I've ordered AT&T Air on the assumption that this will not be fixed shortly, although I'd really like to see it fixed.