I noticed this today after the systemd update and after I rebooted - stunnel package fails to create /run/stunnel and so stunnel.service won't start as it cannot chroot to /var/run/stunnel.
stunnel was updated for me on 10/21 from 5.03 to 5.06. Machine has been rebooted since then - so it -seems- like a change happened in systemd which triggered this, but I'm not sure.
Work around is to add these 2 lines to /etc/systemd/system/stunnel.conf before the ExecStart line:
ExecStartPre=-/usr/bin/mkdir /run/stunnel ExecStartPre=/usr/bin/chown -R stunnel:stunnel /run/stunnel
Probably just a minor package bug.