VZW Ellipsis 8: "Wifi Connection Failure"


I have a series of Linksys WRT1900AC routers (V1 & v2) in my two houses, which up until a month ago ran the stock Linksys firmware. Switching over to OpenWRT across the board, version 21.02, everything is happy (RPIs, printers, desktops, laptops, phones, etc.) except one tablet... a Version Ellipsis 8 running Android 5.1.1, which just refuses to connect to the WiFi now. It fails with a 'WiFi Connection Failure'.

Same hardware, approximately same configuration, only change was the OpenWRT firmware. I even brought the tablet from one house to the other to get the same results. I have double and triple sanity checked things for days.

The tablet has limited options, but it clearly can handle WPA2-PSK. Setting either WPA-PSK or WPA2-PSK on the router don't seem to help.
Cipher is set to automatic. 802.11r is enabled.

I got years of Linux/networking experience... but I'm still getting used to the OpenWRT features. It would be great to be able to examine the logging from the WPA handshake... but I haven't gotten that far yet, as in 2 decades of WiFi experience, I've never had to watch the process from that side.

Anyone see a problem like this? Any ideas?