Explanation
Jitter is most likely causing the issue of intermittent one-way audio and dropped conversations for the company that uses VoIP telephones. Jitter is a variation in delay of packets arriving at the destination. It can cause choppy or distorted audio quality for VoIP applications, especially over WAN links that have limited bandwidth and high latency. The recommended jitter for VoIP is less than 10ms1. The company has recorded ping times that exceed 50ms, which indicates high jitter and latency on their network. References:
https://www.voip-info.org/voip-jitter/ 1

Explanation
A network access control (NAC) appliance is a device that checks the enrollment and compliance state of devices that try to access the network resources. It can deny, quarantine, or restrict the access of non-compliant devices based on predefined policies1. A device can be considered non-compliant if it does not meet the security requirements, such as having the latest patches, antivirus signatures, firewall settings, or encryption standards. In this scenario, the user's laptop may have been labeled as non-compliant by the NAC appliance because it was out of sync with the network policies after working remotely for a long time. The user connected to the guest network, which is usually less secure and isolated from the corporate network, and updated the patches and software, but that may not be enough to satisfy the NAC appliance. The user may need to enroll the device again, or contact the IT support to resolve the issue.
References1 - Network access control integration with Microsoft Intune | Microsoft Learn

Explanation
It does this by using a two-level hierarchy of switches, where the spine switches connect to the leaf switches, which in turn connect to the end hosts. This reduces the number of hops a packet must take from one host to another, thus reducing latency. According to the CompTIA Network+ N10-008 Exam Guide, the Spine and Leaf topology is a modern architecture that is used to reduce latency in large networks.

The users are unable to navigate to websites on the internet but can access local network resources, indicating a possible DNS issue. The ping command result showing "TTL expired in transit" suggests that packets are not reaching their destination due to a DNS misconfiguration that is not resolving website names into IP addresses correctly3. A possible solution is to check and correct the DNS server settings on the network devices4.