For me, I resolved the problem by linking the effected inboxes together and then un-linking them again (making sure there are no unread emails before you unlink).

The issue seems to have been...

Extra thanks all round as I had exactly the same problem and it was WinRAR too. Disabled the shell integration on WinRAR and everything is fine now :)

I'm now in the same position of doing just this after buying a new computer. So, for me I have copied over 92GB of files from the OneDrive folder on my old PC to the new one before launching...

Try uninstalling Skype Video by right-clicking on it in the start menu and selecting uninstall and see what happens to your disk utilisation
;)

(And if you still need Skype, use the normal Skype...