Boo (as in the rasp chant, not for Halloween)
I had gone through a remote libxcrypt upgrade merge and it failed at some apparently unrelated package (same problem as
814140. Little did I know that glibc upgraded to -crypt or something but not openssh/sshd. Due to apparently saving the old glibc that openssh was linked to, it seems to still start fine. However when it tries to fork sshd when someone connects, it fails, I'm thinking it tries to dynamic link to the new glibc with crypt() missing! So I lost access to connect to the remote machine after exiting out of an existing session.
Rebuilding openssh restored operation.
Word of the wise: login to machines multiple times and do not logout until after you verified sshd. Also due to the #*@(#&%!@ing NAT timeout issue, make sure you keepalive everything... *groan*
Got lucky this time but got this close to having to make a service call...