CPU utilization is a metric that measures the percentage of time a CPU spends executing instructions. When the logging level is set for debugging, the router may generate a large amount of logging data, which can increase CPU utilization and cause the router to stop responding to requests intermittently. Reference:
Network+ N10-008 Objectives: 2.1 Given a scenario, troubleshoot common physical connectivity issues.

Explanation
802.11a/b/g/n/ac wireless networks operate in two frequency ranges: 2.4 GHz and 5 GHz. The 5 GHz frequency range supports more channels than the 2.4 GHz frequency range, making it a better choice for high-density wireless networks.
References: CompTIA Network+ Certification Study Guide, Sixth Edition by Glen E. Clarke

A split-tunnel VPN is a VPN feature that allows remote users to access network resources while only redirecting necessary traffic through the VPN tunnel. A split-tunnel VPN enables users to choose which applications or websites to secure with the VPN and which to connect normally through the internet. This can improve performance, conserve bandwidth, and avoid compatibility issues with some services that depend on the user's location. A split-tunnel VPN can also allow users to access local devices or resources that are not accessible through the VPN.