Package: initscriptsVersion: 3.06-4devuan3
The header field for Default-Stop in rc.local is empty so do_stop is never run which means /etc/rc.shutdown isn't run either.
Modifying these lines thus:

# Required-Stop :        $all
# Default-Stop:            0 6

then running:
# update-rc.d -f rc.local remove
# update-rc.d rc.local defaults

saw it begin to work as expected, don't know if that exact change is ideal for all circumstances, but something like that seems to be required.

Also "aptitude show initscripts" says the homepage for the package is https://github.com/slicer69/sysvinit but the initscripts aren't hosted there, only the sysvinit package itself.