I have a number of

Sonoff Basic 

Sonoff POW 2

Sonoff T0US  -which all connect to any of the five TP-Link routers I have 

The new Sonoff POWR316 and my NetHome Plus EU-OSK105 cannot connect to any TP-Link AP in my network.

I disabled 5 GHz to illuminate the mix, and tried all Security settings, but none allows connection

Termite software reports as follows:

00:09:40.154 WIF: Connecting to AP1 ERASMITV in mode  as tasmota-6AC4C4-1220...
00:09:43.480 WIF: Connect failed as AP cannot be reached
00:09:44.508 WIF: Connecting to AP2 ERASMI in mode  as tasmota-6AC4C4-1220...
00:09:56.833 WIF: Connect failed with AP timeout

I also tried the IoT Network on the TP-Link - Makes not difference. The TP-Link does not allow the Sonoff to connect
 

When I use a pocket LTE router that connects to TP-Link first and serves WiFi the Sonoff and NetHome connect fine

https://community.tp-link.com/en/home/forum/topic/615104

this URL reports exactly the same issue.

When will TP-Link sort it out

Any suggestions to resolve this so I can use IoT on TR-Link