My apology - I misunderstood - I was referring to the extension package.
That is a Windows issue - has nothing to do with Manjaro - so your question is better asked at VirtualBox Forum. It could be a bug in the guest additions.
On your host Install the package virtualbox-guest-iso.
Restart your guest and use the built-in upgrade function as illustrated in the screenshot below
Screenshot
If that doesn’t do it - you should use the VirtualBox Forum.