When macOS Sierra was released over two months ago, there were two serious conflicts which could, and did, result in loss of data: with Fujitsu ScanSnap software, which has now been fixed, and with Dropbox. This article examines how those issues with Dropbox have been resolved.

Although updated versions of the Dropbox desktop app have been released since September, Dropbox’s detailed advice to users has changed little over much of that time. Dropbox still works, but it is still possible to use it in a way which is likely to result in data loss, according to its own support article.

To use Dropbox safely when you are running macOS Sierra:

• You should ensure that you have updated to 10.12.1 (although nowhere does the support article even mention that update, as it was written before its release, and has not been updated in the light of it).
• You should leave Dropbox in its default location, and not move it to the Desktop or Documents folder.
• You should avoid using any settings which might move files from your Desktop or Documents folder to iCloud storage (see below).
• You should avoid using any configuration in which iCloud and Dropbox might synchronise the same files.
• Don’t rename your Dropbox folder; leave it named simply as Dropbox.
• If you’re taking screenshots, avoid turning Dropbox off, or those shots may be replaced by iCloud placeholder files and then synced to Dropbox when it is enabled again. I presume this would only occur if you are also using iCloud syncing as well as Dropbox.
• Don’t use “symlinks” (presumably any type of alias) in your Dropbox, particularly those which might point to files or folders in the Desktop or Documents folder.
• When installing Dropbox, give access to Dropbox to Accessibility when asked. Dropbox uses Accessibility for the Dropbox badge, part of its integration with Microsoft Office.

The root cause is that Dropbox sync and iCloud sync, such as that in the Optimized Storage feature of Sierra, remain incompatible. If you have enabled Optimized Storage for your Desktop and Documents folder, then when Sierra considers that your storage (internal drive) is getting short of space, it will automatically start to move files from those locations into iCloud. When it does that, it leaves a placeholder file, with the extension .icloud, where the original file was; this functions like an alias.

If Dropbox is also trying to sync those files with your remote Dropbox storage, then it (still) cannot cope with the fact that those placeholders are not proper documents. Let’s say you had an important document MyFile.doc on your Desktop, which you were syncing with Dropbox. Dropbox will keep a copy of that file on its remote servers for you. If Sierra then decides that MyFile.doc is taking up space which it needs to free, it may move it from your Desktop to iCloud, leaving an empty placeholder file in its place. When Dropbox next syncs, it will assume that it should replace MyFile.doc with that placeholder, so your Dropbox copy of the original file will be replaced by the placeholder file.

In the worst case, you could find that many of the files stored in Dropbox have been replaced by empty placeholders. If you were then to try to retrieve those files, you would find that their contents have been completely lost.

If you are worried that this may have happened already, search your Dropbox for files containing .icloud (or .iCloud). If you find any, you must restore the original version of that file from iCloud, and then reconfigure Dropbox and Sierra to ensure that it cannot happen again. If you think that you may have lost data, contact Dropbox support immediately so that they can work with you to minimise data loss.

For such a widely-used service, these remaining issues are shocking. It is hardly technically challenging to tell the original file, an alias, and an iCloud placeholder apart, yet Dropbox still appears unable to, and allows situations in which data loss has already arisen. Although the chances of this happening may have reduced in the ten weeks since macOS Sierra 10.12 was released, for such a popular product to continue to gamble with your data is inexcusable.

It looks like Dropbox doesn’t care about your business.