> Nobody is able to get more information, or maybe nobody wants to dig this issue. It would be better to get the real cause of the issue,

Well, it looks like a libc or kernel bug, and we probably can't do
much about it. Just falling back to mutex + condition variable instead
of POSIX semaphores does the trick, so I'll say just avoid POSIX
semaphores altogether on AIX and we should be fine. People could
report this to their AIX vendor, but they should definitely consider
dropping this terminally broken platform and switch to, let's says,
Linux or BSD...