I have a similar problem, when I try to install mb-blocks
via Composer I get the Failed to decode zlib stream, here is the full error:
- Installing meta-box/mb-blocks (master): Downloading (100%)
Failed to decode response: Failed to decode zlib stream
Retrying with degraded mode, check https://getcomposer.org/doc/articles/troubleshooting.md#degraded-mode for more info
Downloading (100%)
Downloading (100%)
Downloading (100%)
[Composer\Downloader\TransportException]
Failed to decode zlib stream
I've read in the Composer documentation that this could be a network problem, is everything ok with packages.metabox.io?