This is the current depth of the reliable transmit queue -- EIGRP packets like updates and queries that require acknowledgement, still waiting to go out this interface. Because reliable packets carry route updates, a persistently deep reliable queue means topology changes are being delayed from propagating to neighbors, directly slowing convergence during a link flap elsewhere in the network. A reliable queue depth of 25 during a large topology change is expected and self-clears, but the same depth during steady state signals a stuck neighbor.