While having your breakfast in a regular morning, a close friend of your calls you on the phone telling you in a very worried voice that he received a letter from the National Telecommunications Office regarding the WiFi network of his caf and due to something related to the military he has to pay a fine of 10.000 TL! He tells you that he is on his way of paying this fine but he requests you to urgently go to his caf and try to fix this problem whatever it is.

Not happy about your breakfast being interrupted, you go to the caf and check the WiFi network to see if anything is problematic. You see that there are A LOT OF WiFi networks around the caf belonging to different shops but it is very clear that your friends WiFi network has by far the highest throughput and lowest interference. The APs are using 5GHz band and support 802.11ac. According to the host working in the caf, the APs have been recently changed with these new shiny and expensive looking ones. She tells you that, before these devices are installed the WiFi performance were horrible but now everybody is extremely happy with the WiFi and they even have more customers due to the high speed of their WiFi network.

What caused the initial problem and how can you solve it? Explain.