[gentoo-user] emerge --resume finds an old resume rather than the previous one

I have a shell script which loops on failure from emerge to use
--skipfirst --resume to continue as much as possible.  Every once in a
while, it gets forgetful and picks up an emerge from several days
previous to try to resume instead of the one that just failed.  This
is pretty annoying.  It started several months ago, sporadically, and
seems to be happening more and more often, but not always, and not in
any pattern I can discern.

This is sys-apps/portage-2.1.6.13 on ~amd64.

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