Random connect failures with openssh-6.7p1

[Jay Rouman]

I have been experiencing random connection failures after upgrading to
openssh-6.7p1 from 6.6p1.  The server is built against openssl-1.0.1j
and is running on a Slackware-14.0 machine.  The client is VX-ConnectBot
1.7.1-41.beta.  I am using the beta version because it is the only one
which supports ecdsa public keys, which is what I am using to
authenticate.  The symptom is that ConnectBot prints:

Connecting to <host>:22 via ssh
Verified host 'EC' key: <blah>

Then it freezes.  If you use the Disconnect option, you can try again
and it may or may not complete the authentication.  If it works, the
rest of the session is fine.  I have observed the same problem on two
Android devices, a Motorola Maxx phone and a Nexus 7 (2013) tablet, so I
don't think it's funky hardware.  6.6 built against the same openssl
works every time.

I have debug logs of a failed and successful logins but I am not sure it
is appropriate to post them here and I don't know enough for them to be
meaningful to me.  I have been through several iterations of openssh
with this ConnectBot client and the ecdsa key and everything has been
fine up until now.  Development on VX-ConnectBot seems to have stalled
so upgrading the client isn't an option.
-- 
Jay Rouman (jsr at dexter.mi.org jsr at edzone.net)