This Knowledgebase article provides information about the Sweep Synchronize Task.
The File System Sweep Synchronize task start/stop events can be observed in the Neverfail Heartbeat Management Client Event panel.
This can occur when the user has either added a file filter for files that were in use on the passive server or when services are left executing on the passive server that were opening files denying access to other processes such as nfserverr2.
In some circumstances, if files cannot be synchronized by the FSM such as Apply being denied access to a file, then the FSM can find itself in an endless loop trying to synchronize files that it can't synchronize.
In these situations, the user should remove the offending files from the protection set or determine why the files cannot be synchronized on the passive machine.