Discussed here:
https://forums.whonix.org/t/cannot-download-hardened-tor-browser-using-tor-browser-updater-whonix
Don’t use a VPN without reading and going through the documentation. And if you go through the documentation, you will know why that happens and how to prevent that.
The very short exemplification why that is so is because Whonix uses stream isolation by default which has the disadvantage that combination of tunnels such as VPNs becomes more difficult and requires documentation.