I've had the same problem with:
OpenSSH_7.9p1 Debian-9, OpenSSL 1.1.1b 26 Feb 2019
OpenSSH_7.9p1 Ubuntu-9, OpenSSL 1.1.1b 26 Feb 2019
including the freeze at
debug1: Sending env LANG = en_US.UTF-8
which cannot be stopped by Ctrl-C. After waiting a while I once got:
packet_write_wait: Connection to [ip] port 22: Broken pipe
before the process ended
I was, however, able to connect to the same server using:
OpenSSH_7.4p1 Debian-10+deb9u6, OpenSSL 1.0.2r 26 Feb 2019
OpenSSH_7.7p1 Ubuntu-4ubuntu0.3, OpenSSL 1.0.2n 7 Dec 2017
where I got the same message,
debug1: Sending env LANG = en_US.UTF-8
but then it immediately went to command prompt rather than freezing
Last login: Tue Mar 19 17:54:25 2019 from [ip]
It seems that the problem was introduced to OpenSSH between 7.7 and 7.9