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Navigate to your "Manage Forms" feature
Set the following filters
Users: "admin", "web users", "unknown users"
For case imports specifically you can select "web users" only
Check the box for "Show Advanced Options"
Check the option for "Unknown Forms"
Leave the "Choose Unknown Form" selection as "Show All Unknown Forms"
Set the dates when you think the system actions took place
Set the Archived/Restored filter to "Normal Forms"
Find all the forms in the results section which are "System Forms"
You can open and review these forms to identify whether these are the system actions you are looking for.