People wise in the ways of Workflow say:

"Guess #1 would be the activity log rolled over in the middle of the interval somewhere. Shouldn't cause any issues. The activity log rolls over something like every 500k rows."

Guess #2 would be much much worse things like replacing the repository's DB with an older copy (while WF Subscriber was running).

Though, if it happens every 2-4 minutes, then neither guess is likely. Probably worth opening a support case and attaching a chunk of Subscriber logs covering that interval of time. (By default, the logs would be in C:\ProgramData\Laserfiche\WF\ServerData\SubscriberLogs\<Subscriber Machine Name>\<Repo UUID>)