When a user reports that internet access is not working, it is important to first determine if there have been any recent changes to the network or the user's computer that could have caused the issue. This could include changes to the network configuration, the installation of new software or hardware, or other events that could have impacted the user's ability to access the internet. By determining if anything has changed, the administrator can narrow down the possible causes of the issue and focus on addressing the most likely cause.

Channel overlap is a situation where multiple wireless networks use the same or adjacent frequency channels, causing interference and degradation of performance. According to the image, the corporate SSID is using channels 9, 10, 11, and 6, which are overlapping with each other and with other networks in the area. This can reduce the signal quality and strength, increase the noise and latency, and cause dropouts and connectivity issues. To avoid channel overlap, it is recommended to use non-overlapping channels, such as 1, 6, and 11, in the 2.4 GHz band, or to switch to the 5 GHz band if possible12.
Reference
1 - What happens when wifi channels overlap? - Server Fault
2 - Is it better to use a crowded 2.4GHz Wi-Fi channel 1, 6, 11 or "unused" 3, 4, 8, or 9? - Super User

The document that would most likely be used to review disaster recovery information for a system is a business continuity plan (BCP). A BCP is a document that outlines the procedures and resources needed to maintain or resume critical business functions in the event of a disaster or disruption. A BCP typically includes a disaster recovery plan (DRP), which is a subset of the BCP that focuses on restoring IT systems and data after a disaster. A BCP also covers other aspects of business continuity, such as risk assessment, business impact analysis, emergency response, crisis management, and testing. Reference: CompTIA Network+ N10-008 Certification Study Guide, page 346; The Official CompTIA Network+ Student Guide (Exam N10-008), page 13-9.

A site survey is a process of analyzing the wireless environment and determining the optimal locations, configurations, and parameters for access points (APs). A site survey can help identify sources of interference, dead spots, signal strength, and coverage areas1.
AP placement is the physical location of the APs in relation to the wireless clients, walls, ceilings, floors, and other obstacles. AP placement affects the signal quality, coverage, and performance of the wireless network2.
The network administrator should check the site survey and the AP placement first when troubleshooting intermittent Wi-Fi connectivity issues, as these factors can directly impact the wireless signal and user experience.
EIRP (Effective Isotropic Radiated Power) is the total power radiated by an antenna in a specific direction. EIRP is affected by the transmitter power, cable loss, and antenna gain3. EIRP is not the first thing to check, as it is usually configured according to the site survey and the regulatory standards.
A captive portal is a web page that requires users to authenticate or accept some terms and conditions before accessing the wireless network. A captive portal can be used for security, marketing, or legal purposes. A captive portal is not the first thing to check, as it does not affect the wireless signal or connectivity, but only the access to the network resources.
SSID (Service Set Identifier) is the name of a wireless network that is broadcasted by the APs. SSID assignment is the process of configuring the SSID on the APs and the wireless clients. SSID assignment is not the first thing to check, as it does not affect the wireless signal or connectivity, but only the identification of the network.
AP association time is the time it takes for a wireless client to connect to an AP and establish a wireless link. AP association time is not the first thing to check, as it does not affect the wireless signal or connectivity, but only the initial connection process.
Reference:
1: Site Survey
2: AP Placement
3: EIRP
4: [Captive Portal]

"Using special STP frames known as bridge protocol data units (BPDUs), switches communicate with other switches to prevent loops from happening in the first place. Configuration BPDUs establish the topology, where one switch is elected root bridge and acts as the center of the STP universe. Each switch then uses the root bridge as a reference point to maintain a loop-free topology."