The rc.d scripted does seem outdated which expected since you seem to be running a 9.3 Jail (as you state in the title)
The minimum supported version for FreeBSD is 11.2 however (See the FreeBSD requirements here: https://support.plex.tv/articles/200375666-plex-media-server-requirements/)
Some users reported it still worked (and by that I mean started, unsure about full functionality) on 11.1, but that is no longer the case and the minimum supported version is 11.2, more info here Server doesn't restart after 1.15.6.1079 update
