Quick solution:

With this kind of error, I usually start by raising the postBuffer size by:

git config --global http.postBuffer 524288000

(some comments below report having to double the value):

git config --global http.postBuffer 1048576000

More information:

From the git config man page, http.postBuffer is about:

Maximum size in bytes of the buffer used by smart HTTP transports when POSTing data to the remote system.
For requests larger than this buffer size, HTTP/1.1 and Transfer-Encoding: chunked is used to avoid creating a massive pack file locally. Default is 1 MiB, which is sufficient for most requests.

Even for clone, that can have an effect, and in this instance, the OP Joe reports:

[clone] works fine now

Note: if something went wrong on the server side, and if the server uses Git 2.5+ (Q2 2015), the error message might be more explicit.
See “Git cloning: remote end hung up unexpectedly, tried changing postBuffer but still failing”.

Kulai (in the comments) points out to this Atlassian Troubleshooting Git page, which adds:

Error code 56 indicates a curl receive error of CURLE_RECV_ERROR which means there was some issue that prevented the data from being received during the clone process.
Typically this is caused by a network setting, firewall, VPN client, or anti-virus that is terminating the connection before all data has been transferred.

It also mentions the following environment variable, order to help with the debugging process.

# Linux
export GIT_TRACE_PACKET=1
export GIT_TRACE=1
export GIT_CURL_VERBOSE=1

#Windows
set GIT_TRACE_PACKET=1
set GIT_TRACE=1
set GIT_CURL_VERBOSE=1