Discontinued Scheduled Batch Campaigns

Hello trustworthy Marketo community!

Over the past few weeks I've noticed some of our regularly-scheduled batch campaigns have stopped sending. Because they're not falling into the list of Idle Triggered Campaigns, I haven't found a list of these campaigns that are discontinued. We always have qualified leads for these campaigns. Also, I can go into the campaigns and re-schedule them and everything goes as it should after that. What causes these campaigns to stop running? Is there a way I can prevent this from happening?

Thanks!