Again this never worked natively in PMS, not with FreeBSD you were likely dong this via some script/3rd party software.
If we never added code for this how could it have worked? The approach we use for linux is not supported by FreeBSD and AFAIK never was.
One of our devs attempted to look into using kqueue and it wasn’t worth it, see Properly implement kqueue to allow PMS to auto-update library on filesystem change (FreeBSD) (back in 2016), so please trust me this never worked and unless FreeBSD adds support to inotify I’d say its unlikely too, this is actually the case with other software’s its one of the biggest gotchas in porting to BSD.
I am a use and fan of BSD for years and this is one of those things I really which they improved on. I looked into fswatch, for reasons other then plex since it cross platfroms and found that it still uses kqueue as a backend and so as similar limitations:
The kqueue monitor, available on any *BSD system featuring kqueue, requires a file descriptor to be opened for every file being watched. As a result, this monitor scales badly with the number of files being observed, and may begin to misbehave as soon as the
fswatchprocess runs out of file descriptors. In this case,fswatchdumps one error on standard error for every file that cannot be opened.
FreeBSD is IMHO better than linux in many things, but this is by far not one, and from what I’ve picked up on mailing lists/forums there’s no plans on improving this soon 
That said depending on how you add media it shouldn’t be hard to automate calling the scan on a library (tools like sonnar i.e. do this)
