I upgraded libc6 on a armhf box running a rather stale version of
testing, due to installing some package that needed the new version:

2022-04-12 18:23:06 upgrade libc6:armhf 2.32-4 2.33-7

After this partial upgrade, sshing to the host failed. With -v,
the last line displayed was:

ssh debug1: expecting SSH2_MSG_KEX_ECDH_REPLY

I fell down a rabbit hole of old bug reports about connections failing
(or hanging) at that point, which seemed to indicate a MTU or other
networking problem. Notably though, even ssh localhost failed like that,
and it was not hanging like in old reports such as [1], so this seemed
like a slightly different problem.

There was nothing useful logged in the journal.

I resolved the problem with this upgrade:

2022-04-13 11:38:09 upgrade openssh-server:armhf 1:8.4p1-6 1:9.0p1-1

So it seems that something about openssh 8.4p1-6 was broken by glibc
2.33. I'm filing this bug because it seems at least possible that
whatever incompatability that was is still lurking, and will be
triggered again by a future glibs upgrade.

Kernel: Linux honeybee 5.14.0-2-armmp-lpae #1 SMP Debian 5.14.9-2 (2021-10-03) armv7l GNU/Linux