This counts frames that were not transmitted because they encountered a collision outside the normal collision detection window. Late collisions are a specific, well-known symptom of a duplex mismatch, one side full-duplex and the other half-duplex, rather than genuine network congestion, so any nonzero, growing value here is a strong, actionable signal to check cdmipEthernetSpeed against the connected switch port's actual configuration. Seeing this counter increase while cdmipEthernetSpeed is set to fullDuplex100M(5) would suggest the connected switch port is actually running half-duplex, a mismatch that produces exactly this symptom.