Actions will stop due to the following reasons:

• If the action is 'Add to another list', the target list (i.e. the list you've selected to add the subscribers to) may have been deleted.
  
• If the action is 'Push to Zoho CRM', the custom field mapped to Zoho CRM may have been deleted.
  
• If the action is 'Update fields', the custom field may have been deleted.
  
• If the action is 'Assign tags', the tags set for contact assignment may have been deleted.
  
• If the action is 'Remove tags', the tags to be removed from contacts may have been deleted.