The sync appears to be stuck in a endless loop creating the same invoice repeatedly
Update: Autotask has confirmed this is a bug within the API and working on a updated fix.
This problem occurs when the Paid Date is added to the invoice in Autotask before our sync process is finished. As a result, we are unable to update Autotask with the webservice date using the API. To resolve this issue, you should remove the Paid Date, wait for the sync to complete entirely, and then reapply the paid date once you are certain that the sync is finished.
Here is an example of an invoice that can cause sync issues. In this case, the Date Paid field is filled out, but the Web Service Date is empty.
We actively monitor for sync loops, if we detect a sync loop your sync will be paused until this is corrected.