This read-only PerfCounter64 counts packets discarded due to lookup failure on this link aggregation group, per its source description, meaning packets the device could not forward because a table lookup, such as a MAC or FDB lookup, came up empty. A rising count tells an administrator that traffic is arriving for destinations the switch hasn't learned or that a hardware forwarding-table resource is being exhausted. For example, seeing cmLagHistoryLkupFails spike shortly after cmLagHistoryESDE also spikes would suggest a learning-table flush event caused a temporary wave of unresolved lookups on the LAG.