You'd want to review your cache settings in ACP -> System -> Advanced Configuration -> Data Storage. If you're using file system, something is getting corrupted. This may be that your file system storage is full, something is not writing correctly, or something else entirely. First you will want to check your storage for your server / storage configuration. If you have plenty of space, you may wish to try to switch to database temporarily to see if this corrects the issue. If it does correct the issue, you will want to contact your hosting provider for assistance on why your file storage is not writing correctly or becoming corrupted.