The client drivers are faulty and should be upgraded is the likely problem for the laptop that can see and connect to 2.4 GHz APs, but does not even see 5 GHz APs. The client drivers are the software components that enable the wireless adapter of the laptop to communicate with the operating system and the network. The client drivers are responsible for scanning the available wireless channels, detecting and connecting to the access points, negotiating the security and data rate parameters, and transmitting and receiving data frames. If the client drivers are faulty, outdated, or incompatible, they may cause various issues with the wireless performance and functionality, such as low data rates, poor signal strength, frequent disconnections, or inability to see or connect to certain access points or channels.
One of the possible causes of faulty client drivers is that they do not support or recognize some of the features or standards of the 802.11ac technology, such as wider channel bandwidths, higher modulation schemes, or DFS (Dynamic Frequency Selection) channels. This could explain why the laptop can see and connect to 2.4 GHz APs, but not 5 GHz APs, as 802.11ac operates only in the 5 GHz band and uses channels that are wider (up to 160 MHz) and higher (up to channel 165) than those used by previous standards. Moreover, some of the
5 GHz channels are subject to DFS rules, which require the access points and client stations to monitor and avoid using channels that are occupied by radar systems or other primary users. If the client drivers do not support or comply with DFS rules, they may not be able to see or connect to access points that use DFS channels.
To solve this problem, the client drivers should be upgraded to the latest version that supports and is compatible with 802.11ac features and standards. This can be done by downloading and installing the updated driver software from the manufacturer's website or using a device manager tool. Upgrading the client drivers may also improve other aspects of wireless performance and functionality, such as data rates, signal strength, security, and stability. References: 1, Chapter 12, page 493; 2, Section 8.1