There are several Activity types that are not extracted using the Bulk Extract API. These are:
1. Create Task (create a task in SFDC)
2. Sync Person Update (in SFDC)
If there are any errors when you're creating a Task in SFDC they are shown in the Activity log next to the Create Task Activity, the error is normally a response from SFDC. This is the only way to retrieve these errors in any automated way, however Marketo does not provide these in the extract which is very surprising.
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