*ALWSAV attribute is not mentioned athttps://www.ibm.com/support/knowledgecenter/ssw_ibm_i_72/ifs/rzaaxtmpdir.htm
There exists the option to submit feedback for the page; now in the
form of the /comments/ section instead of a feedback-button.
However if someone reveals that the ATR(*ALWSAV) for /tmp has changed
to have VALUE(*NO), then I may be motivated to find someone to whom I
can report what I concluded was the problem for the OP; i.e. suggest to
somethat that IBM might still have an issue that may not yet have been
addressed, except tangentially and merely masked by chance, because
anyone could choose to [re]include /tmp using CHGATR [unless again,
though doubtful, that explicit change request is prevented].
I scanned the Memo to Users for a few releases back and failed to find any
such thing. I did have to kneecap a few people at IBM to get them to stop
changing the /tmp "restricted rename and unlink attribute". This was
blowing up email programs where UserA would send an email but the IBM user
associated with QMSF and/or SMTP could not delete said stub when done. At
some release they thought it would be a good idea to change this attribute
at IPL time.