Solution – Use the Free Download Manager.
This will make sure your downloads finish properly. Many internet connections time out and although it appears the download is complete, it has been corrupted. You can find the Free Download Manager here https://www.freedownloadmanager.org/
There is a version for both Windows and MacOS at the download page here:
Also for a better chance of success, only download 1 part at a time instead of all of them together.
Resuming downloads using Chrome of Firefox does not work and will end up as a corrupt download.