Hi @shadowcat412; welcome to our Community and thanks for flagging this.
Just to make sure we're troubleshooting the right thing here, could you clarify if you're referring to the desktop app that's shown within your system tray or if this is about the Dropbox for S Mode for Windows 10 devices?
Could you also let me know the device's exact OS and build and the version of our app?
The moving or copying action is handled by your device's OS so there might be a pending update you need to perform.
Strange workaround may provide a hint to the issue:
Click file to highlight it
Drag file to move it
This is the reason why the issue only appeared some of the time. When the file was already highlighted, it could be dragged and dropped. If it wasn't highlighted, then drag and drop doesn't work. Very tedious to always click before moving a file.
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