Hey @JEM58, thanks for bringing this to our attention.
If the new file name appears on your account online, that means that the change has synced with your account, but not with your other two devices, so that's where the sync issue must lie.
Can you check the sync status and version of the Dropbox app on your laptop and your second desktop?
You can do so, by hovering over the Dropbox icon in the system tray/menu bar.
Let me know what you find and we'll go from there.