Hello, I have a Deco XE75 network (3 units) and a weird 6 GHz problem.

Symptoms:
When I have all 3 frequency bands enabled (2.4 + 5 + 6 GHz), and all 3 are using the same SSID,

I have the strange phenomenon that some of my WLAN clients have issues connecting to the 2.4 or 5 GHz band.

Sometimes they can, but most of the time they can't connect.
Most of the time the Deco SSID isn't visible in the Windows SSID list (it does display a "Hidden network" SSID),

or sometimes the SSID is visible but the device simply can't connect to it.
 

Some devices = 2 HP laptops, running Windows, but different laptop models with different WLAN NICs though: 
Realtek RTL8723DE 
Realtek RTL8852BE
These devices are not WiFi 6E compatible (not even WiFi 6) by the way.

So I'm not talking about issues connecting to 6 GHz, it's issues connecting to 2.4 and 5 GHz.

Troubleshooting:
For troubleshooting, I modified several parameters, both on Deco and on the client WLAN NICs, to no avail.

What finally 'solved' the issue was renaming the 6 GHz band SSID on Deco, so it has a different SSID than the 2.4 / 5 GHz SSID.

Now connecting to the Deco SSID works like a charm + the "Hidden network" SSID is gone from the SSID list.

It also works when I disable the 6 GHz band.
However, I don't understand why having the same SSID should be an issue (for some clients, which don't even support the 6 GHz band).

Has anyone else experienced this issue, or can explain what the cause is?