A network engineer is troubleshooting an EIGRP adjacency failure between R1 and R2 in AS 100. Both routers have matching AS numbers and are directly connected on the same subnet. The engineer runs 'show logging' on R1 and sees the message: '%DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 10.1.1.2 (GigabitEthernet0/0) is down: K-value mismatch'. Interfaces are up and pings succeed. What is the most likely cause?