Hallo @Ash85 

Can you check in de Box 12 WiFi settings if the Bandwidth setting is set to 80 MHz for the 5GHz WiFi, that’s a likely cause of the connection problem for that laptop.

You can find here how to login to the Box 12:

Thanks a lot for your msg. Is there any other way for me to find this out? I tried to go through all the steps mentioned on your provided page, but at the end it keeps saying wrong log in info, so I cannot log in to my kpnmodem to check this. Very strange! because I never used this before and I just put the Admin password written on backside of my modem, but it does not work at all.

Sometimes logging in to the modem only will work using this link: http://192.168.2.254/2.0/gui/#/login

and/or with another browser like Firefox, Edge or Safari.

Yesss. I suceeded to log in and set  a new password via your new link. 

I checked the bandwidth for 5GHz was set at 20 MHz ( same was for 2.4 GHz). So I changed it to 80 MHz for 5 GHz as you suggested but it gives an error that i shoud change the value of SSID and security key. Any idea? Thanks a lot.

Yes, that’s something other users also get sometimes, just change it by putting a 1 behind the SSID en the security key, save that and change it back to the original, it then shouldn't complain about that anymore.

This has nothing to do with your bandwith. This has do with the new wifi 6 protocol that can't work with your business laptops sometimes has to do with a outdated network hardware card. You should try changing your wireless mode to 802.11b+g+n on the 2.4Ghz and on the 5Ghz 802.11a+n+ac.
Note that this will indeed change your internet speeds for just one device to connect, so is it worth it to downgrade; for example a 1Gbit line for 1 laptop, i dont think so.

Some Intel networkcards can’t connect when the 5GHz bandwidth is set on AUTO and uses 20 MHz, so it certainly can be the problem, it's better to try that first because it also makes the 5GHz band faster that way.

The AUTO function is for channels not bandwidth. And the Mhz is for increasing the bandwidth's reach. The higher the number in MHz the faster the network so by putting it to 20 it would decrease the 5GHz speed.
However certain devices do not connect with 5GHz radio. But a laptop can certainly do this. More like domotica devices like doorbells or catfeeders etc etc can’t connect to 5GHz and should have a seperate SSID for 2,4GHz in order for this to work. However that is not the case right now. Were talking about a nummer of business laptops that cant connect to the V12 modem. Maybe due to that they can't function with the new Wifi6 protocol or that they are so setup by the company that they require permission from the administrator in order to connect to a home network. But since the laptop can connect to other wifi's it more certainly would be the wifi6 protocol issue which should be changed to the 802.11b+g+n for 2.4GHz and the 802.11a+n+ac for 5GHz.

But since only the poster of this forum article can only LIKE the messages we submit to him. We cant know if it actually worked.

This is the standard setting for 5GHz bandwidth and the Auto setting often chooses 20 MHz which is the problem for some networkcards not connecting or connecting and then disconnecting.

Thanks for your tips. I will try both suggestions this weekend. 

Hi @Ash85, did you manage to get it working?

Hi, yes it works but very surprising, before I change any parameter that has been advised on top, for the last time I left the wifi and reconnected, till now it never disconnects anymore. VERY STRANGE! because I had done this multiple times before and problem did not solve! if it happens to disconnect again, I will certainly try the advises given on top! thanks a lot!