Apple has started sending out emails to members of the AppleSeed beta testing program informing them of ongoing maintenance to iCloud Drive. According to the message, due to the in-development nature of the updated iCloud backend, users should expect to see more downtime than they experienced with older versions of OS X.
Unlike the developer previews, however, Apple notes that these outages are not likely affect files stored in iCloud. Twice previously the company has wiped all data uploaded to iCloud Drive. Of course, it’s important to keep backups of important files, as Apple points out that unforeseen issues with betas could lead to data loss.