Today I tried to export some worlds directly to my Dropbox which is on my D: drive. The game created the .mcworld file, with the file name, but did not give the "exported successfully" notification and the files were all zero bytes.

So after reinstalling Minecraft and failing on several attempts, I chose to save direct to the D: to see if that would work. Which it did.

So I thought, maybe Dropbox was interfering with the export.
So I shut all Dropbox processes down and tried again.
It still failed.

I tried all subdirectories back from the folder I was trying to save to and they all failed with the exception of the root drive folder.

"D:\Dropbox\Foxy No-Tail__Bedrock Realm\World Downloads" - Failed
"D:\Dropbox\Foxy No-Tail__Bedrock Realm" - Failed
"D:\Dropbox\Foxy No-Tail" - Failed
"D:\Dropbox" - Failed

"D:" - Works as expected

Even more bizarrely, any path not including the word "Dropbox" works fine.

For example, changing the O in Dropbox to an I, the entire path works fine...
"D:\Dripbox\Foxy No-Tail__Bedrock Realm\World Downloads" - Exported Successfully

I also had these issues previously in version 1.9 and 1.10 trying to export 3D structure files using the structure blocks. When exporting they created 0kb files with no content.