Hi!
Boxcryptor does not rename folders (or files) on itself. Most likely, the folder has been renamed by another application (e.g. the sync software of your storage provider) directly or in the Boxcryptor drive. Sync software sometimes automatically renames files or folders when a sync conflict occurs, e.g. the same file or folder has been modified at the same time by two different devices.
Anyways, you should be able to manually rename it back to "DOCUMENTS" without problems.
Best regards,
Robert