The root cause is that the SysModStamp for one of the object records (Campaign, Campaign Member, Campaign Member Status) for the record was updated, so, in the perspective of the Sync User, the newly updated (recent SysModStamp time) record needs to be queued up to be synced.
If this is causing some unintended Marketo Trigger Campaign activity, we advise that active Trigger Campaigns be reviewed to make sure that past campaigns are deactivated, and only relevant campaigns are currently active.