Occasionally seen when sshing to a Hurd system:

$ ssh [...]
PTY allocation request failed on channel 0
GNU laplace 0.9 GNU-Mach 1.8+git20180218-486-dbg/Hurd-0.9 i686-AT386
This is the GNU Hurd.  Welcome.  [...]
[No prompt displayed.]
Connection to [...] closed.

That is, we failed to get a PTY allocated.

We currently set up a limited number of translator nodes providing preallocated PTYs (term translator instances), instead of dynamically allocating via /dev/ptmx, for example. (Which might or might not resolve this issue; there might be some resource leak involved?)

Last seen timestamp: 2018-07 (lost exact date).