Hi @Kombinator, welcome to our forum! English is fine! 
I'm not sure why this does not work. Are you using Superwifi punten or any other wifi repeaters?

Hi @Thomas van KPN, thanks for the reply. Yes, I do use superwifi 2, but they are should be fine because checked their bandwidth and it shows 160. The 80mhz bandwidth problem only happens to Kpn Box 12 itself.

Ah thanks,

What software version does your box12 have?
When is the last time you gave it a factory reset?
Could you try that again to make sure you have the latest version? 

SW version is V12.C.23.15.06. Did a factory reset yesterday but no impact.

What is strange is that kpn box shows bandwidth 80 mhz selected but WiFi analyzer app shows that kpn box broadcasts actually in 160 mhz.

What is even more strange: I tried to change the value of bandwidth from 80 to 40 but WiFi analyzer keep saying that despite the value of bandwidth I choose, the actual broadcasted value remains 160.

When I switch back to WiFi 5, the actual broadcasted value changed to 80 (according to analyzer). But again no success to change it to 40 etc. So seems as bandwidths values is out of my control for some reason :D

Ah thanks! I checked this with our colleagues and this seems to be a known issue. This should get fixed with an update. For more information on these updates you can always subscribe to our Product Updates page