A network administrator notices that devices on the network are sending data to an unexpected MAC address, despite the IP address being correct. This could be indicative of which type of issue?

When devices on the network send data to an unexpected MAC address while the IP address is correct, it could be indicative of ARP (Address Resolution Protocol) Spoofing. ARP Spoofing is a type of attack where an attacker associates their MAC address with another device's IP address, redirecting traffic meant for that IP address to the attacker's system. This can lead to a security breach. DNS Hijacking, IP Spoofing, and Packet Fragmentation are different issues with distinct characteristics.