/proc/pid exists but does pid not found in ps

I am seeing a very odd behavior.

/proc/1154/cmdline

exists, and

-0 1154

succeeds, but

-ef | grep 1154

and

/proc | grep 1154

do not show anything. 1154 was a postgres process in the middle of shutdown (or the logs say but maybe they did not get flushed) when the vm was restarted. How is this possible?