As promised, an update:

I've taken the belt-and-suspenders approach and gotten the router working very well for the workload we throw at it. 

1. I installed the beta firmware

2. I set the router to automatically reboot each morning at 4am. All nighttime backup-to-NAS tasks easily complete before this time.

3. I created 3 separate networks: 

(1) 2.4GHZ 802.11B/G/N only, for our older stuff with compatibility issues (like apple homekit plugs), as well as phones (because none of these things access data any faster than my cheap-ass 50Mbps internet connection can provide it) 

(2) 5GHZ 802.11AC only, for our printer, because it wouldn't reliably connect to a 2.4GHZ network or a 5GHZ network with AX enabled

(3) 5GHZ 802.11AX only, for our 3 computers, which benefit from a fast connection to our NAS drive.

It seems to be rock solid. There's only been one time this week when a web page was slow to load on my phone, and it loaded after disconnecting from the wifi.  So that could be my internet service acting up.  I've never had any hiccups with any of the computers, printer, NAS or homekit devices.

I'll probably leave it like this because it serves our needs well. Further tweaking might lead to more success in taking advantage of the router's features, but it wouldn't provide a material benefit to our household. 

@shaywood Speaking to them now. Not installed the beta as I think from reading this, it has the same problems. The settings I posted do seem to work for me, but smart connect is a feature this has that SHOULD work along with auto assignment of channel and bandwidth.

Will see what engineers say. If there were an alternative with better reviews, I would have purchased that already and returned this :)

Just to make sure I'm clear: I did everything described in my  prior message at the same time... I did not wait to see whether the beta firmware solved my problems before setting up the three networks.

I just wanted to quickly get to a setup that works, rather than tinkering with it anymore to find the optimal set up.

Further to my previous post, I'm seeing a similar problem to a couple other people, the 5G channels are completely gone from the router UI. They're not disabled, they're just missing entirely. The weird thing is I can see both channels when I check my phone's wifi, but I can't actually connect to them.

This is just getting silly. I hate to pull out the old chestnut, but I think it's time to return this router and buy a different brand :(

I managed to solve all my issues, I switched to a Netgear Nighthawk, sending the TP AX11000 back :(

@tarund fi you still have this beta, i would like it b/c I am still having this issue.  Much appreciated!!!!

@Tony - do we have an ETA on the official firmware release? Last release for this router was five months ago, and it looks likes we still have a lot of bugs. I think the community here would like to see more support for the flagship router for tp-link.

@tarund Thank you for posting this. I have been watching this thread and have been waiting for a fix. I just applied the beta and am now hopeful this will fix the issue. Link Much appriciated!!!!!

@shaywood @Jerryb I too have a ton of devices on my home network and am so glad someone posted the beta links. I have over 45 2.4Ghz devices as I use a ton of smarthome devices. With anywhere from 45 to 55 connected at a time. Changed some settings with support which seemed to help but now I can see if this beta firmware fixes the issue. If it does will be nice to try out once released an official 1.0.7 FW. Hopefully then we can all set whatever we want and it will not drop.