github ssh fails

[micsthepick]

I can clone a github repository using http, but if I use ssh, it fails due to the following error:

stash: <class 'dulwich.errors.HangupException'>: The remote server unexpectedly closed the connection.
Traceback (most recent call last):
  File "/private/var/mobile/Containers/Shared/AppGroup/82D4665C-C583-4CFC-9945-2919CAD0A4C8/Pythonista3/Documents/site-packages/stash/system/shruntime.py", line 546, in exec_py_file
    exec (code, namespace, namespace)
  File "../site-packages/stash/bin/git.py", line 796, in <module>
    ns.func(args)
  File "../site-packages/stash/bin/git.py", line 505, in git_clone
    repo = Gittle.clone(args[0], args_1, bare=False)
  File "/private/var/mobile/Containers/Shared/AppGroup/82D4665C-C583-4CFC-9945-2919CAD0A4C8/Pythonista3/Documents/site-packages/stash/lib/gittle/gittle.py", line 440, in clone
    repo.fetch(bare=bare)
  File "/private/var/mobile/Containers/Shared/AppGroup/82D4665C-C583-4CFC-9945-2919CAD0A4C8/Pythonista3/Documents/site-packages/stash/lib/gittle/gittle.py", line 407, in fetch
    remote_refs = self.fetch_remote(origin_uri)
  File "/private/var/mobile/Containers/Shared/AppGroup/82D4665C-C583-4CFC-9945-2919CAD0A4C8/Pythonista3/Documents/site-packages/stash/lib/gittle/gittle.py", line 367, in fetch_remote
    remote_refs = client.fetch(remote_path, self.repo)
  File "/private/var/mobile/Containers/Shared/AppGroup/82D4665C-C583-4CFC-9945-2919CAD0A4C8/Pythonista3/Documents/site-packages/stash/lib/dulwich/client.py", line 251, in fetch
    progress)
  File "/private/var/mobile/Containers/Shared/AppGroup/82D4665C-C583-4CFC-9945-2919CAD0A4C8/Pythonista3/Documents/site-packages/stash/lib/dulwich/client.py", line 559, in fetch_pack
    refs, server_capabilities = read_pkt_refs(proto)
  File "/private/var/mobile/Containers/Shared/AppGroup/82D4665C-C583-4CFC-9945-2919CAD0A4C8/Pythonista3/Documents/site-packages/stash/lib/dulwich/client.py", line 168, in read_pkt_refs
    for pkt in proto.read_pkt_seq():
  File "/private/var/mobile/Containers/Shared/AppGroup/82D4665C-C583-4CFC-9945-2919CAD0A4C8/Pythonista3/Documents/site-packages/stash/lib/dulwich/protocol.py", line 201, in read_pkt_seq
    pkt = self.read_pkt_line()
  File "/private/var/mobile/Containers/Shared/AppGroup/82D4665C-C583-4CFC-9945-2919CAD0A4C8/Pythonista3/Documents/site-packages/stash/lib/dulwich/protocol.py", line 152, in read_pkt_line
    raise HangupException()
HangupException: The remote server unexpectedly closed the connection.

other services (e.g. bitbucket) seem to work fine.