'Download all' not always working

This has been happening a lot for me and my doc users recently:
Clicking “Download all” does not download any files. (error message pops up and an empty zip file downloads)
All the files have completed uploading+scanning for malware.
And they can all be downloaded individually. (but this gets tedious when there’s loads of photos and files to download individually!)
(Note the original files are uploaded 2 cross docs away, but I would hope this wouldn’t cause an issue!)
Download all

Not downloaded

I’m hoping this is simple bug which can be fixed. or there’s an easy workaround. Any suggestions?