From our documentation: https://www.akeeba.com/documentation/akeeba-solo/archiver-engines.html#archiver-zip
The ZIP format is the most well known archive format and is integrated in many operating systems and desktop environments, including Windows™, Mac OS X™, KDE and GNOME.
Please note that due to the way the ZIP format is structured and the limitations of PHP and web servers, it is possible that archives generated by the application will appear to be corrupt when opened with a third party extraction utility. They are not. You can either try to configure your third party archiver tool to ignore CRC32 checksums or use our Akeeba Kickstart or Akeeba eXtract Wizard software to perform the extraction.
Furthermore, a lot of third party archive extraction software based on the InfoZIP library such as unzip (Linux, *BSD, Mac OS X), WinRAR and 7-Zip will always report ZIP archives generated by the application as corrupt. This is a bug in their software, as they do not support the official split archive ZIP standard. PKZIP (written by the inventor of the ZIP format) and WinZIP, however, do support the official standard and can extract archives generated by the application.
As you were told by our support and as documented the ZIP archive is not broken, only the CRC32 appears to be. Please use Akeeba Kickstart to extract the backup archive. There are only so many ways we can say it.
If you have a problem extracting the backup archive with Kickstart please file a new ticket.
Nicholas K. Dionysopoulos
Lead Developer and Director
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