Every time I log into gnome, the following error message is logged in the
journal:

checkproc[1942]: checkproc: can not get session id for process 5378!

Note that the process number of checkproc changes every time, however the
problematic process number is always 5378, which I find rather suspicious. By
the time I start a shell, there is no process 5378... if there ever was.

The message immediately following this one in the journal is always:
org.a11y.Bus[1952]: Activating service name='org.a11y.atspi.Registry'
but there is no proof these are related. So I have no idea who is producing the
error message.

I believe such error message need to be improved to mention the name of both
the calling service/process and some information about the process it looks
for.