Why are certain ItemUsage 1Password events not showing up in Panther?
There could be two possible reasons why you are not seeing 1password events in your Panther instance:
Check to see if the ItemUsage events you are looking for are from a private vault. Private vaults will not generate ItemUsage events. You will only be able to see these events if they are from a public/shared vault.
If you are using a public/shared vault and are still not seeing ItemUsage events, check to see what version of 1Password you are on. Any version older than 1Password 7 will not report item usage(e.g exports of vaults or any other actions taken by users).