Right click on the placeholder and see if the Size on disk and Size of file, if it is same, then the placeholder has been recalled but still shows as offline. This means that the placeholders have been corrupt.
You can then delete those placeholders...
You can start a OWA looging on all the CAS servers to see what kind of error you get in the logs and based on that you can further troubleshoot the issue.
You can check the safety copy setting, it can be that the file is being archived and the placeholder is being created on the next day. It can also be that the placeholders are being recalled and the task is recreating them when it starts the next day...
You will have to use the FSAUtility to re-create the placeholders but do check the policy, so that the Delete on Delete is not enabled and hence, deleting a placeholder should not delete the archived files.