Similar issues to this ticket:
#22472: cURL library error #3: malformed
My installation is on an unmanaged VPS, however it is fully updated. Download IDs are set for each site and installed per your instructions. All sites currently using Akeeba fail to update properly. Note: I am using several VPS accounts, all self-configured. I check for and install Ubuntu updates daily. Automatic updates worked fine until 1.3.0. I've checked and my subscription is current with your company.
1. Even though the PHP version is current, it is possible I'm missing a key library. I've researched this, but haven't found anything missing. I can generate valid SHA256 hashes from the command line.
2. Do you have some sort of troubleshooting advice or tool that would help identify the issue?