I’ve got an answer from Duplicator’s support crew. In my case it’s because PHP on Windows does not support file sizes above 2GB. This is a limitation with XAMPP/PHP not Duplicator.
Maybe this helps other users in the future.
I have the same Problem, when I try to run the Installer on local Windows 10 Machines with XAMPP (Apache, MYSQL).
The Installer works well on external Webspace and also under macOS Mojave with MAMP.
“Archive file size warning.
The expected archive size should be around [4.1GB]. The actual size is currently [220.32MB]. The archive file may not have fully been downloaded to the server. Please validate that the file sizes are close to the same size and that the file has been completely downloaded to the destination server. If the archive is still downloading then refresh this page to get an update on the download size.”
