You run an audit report in ShareGate Migrate, but SharePoint only returns a portion of the data. You receive this error:

Events were trimmed on [X] for [Y] Site. Events before this date are missing.

Not Applicable

This is an error message associated to Sharepoint. It occurs when your audit trimming settings are set to Yes. Trimming allows you to keep only a certain amount of logs based on a specified amount of days, and everything before that is deleted.

You can verify this from your top level site settings by going to:

ShareGate Migrate uses the data from audit logs to create the audit reports, so trimming will prevent the logs from being available and we can't produce the report.

Change your audit trimming settings to No, or change the amount of days as appropriate. For more on configuring audit settings, go here.