ssh_exchange_identification: Connection closed by remote host

hey there,

i've a problem with our gitlab-ce.

every time a repo was pushed or pulled, another user will be blocked for about 10 seconds and get a error

git clone ssh://git@example.org/example/example-component.git ssh_exchange_identification: Connection closed by remote host
git clone ssh://git@example.org/example/example-component.git fatal: Could not read from remote repository.
git clone ssh://git@example.org/example/example-component.git 
git clone ssh://git@example.org/example/example-component.git Please make sure you have the correct access rights
git clone ssh://git@example.org/example/example-component.git and the repository exists.

It is a dockerized gitlab-ce with a ssh-tunnel via another host. The tunnel is still working. (direct communication fails too)

• gitlab version 7.9.0
• gitlab-shell 2.6.0

may there is someone which can help

thanks in advance