Using a NAS for original storage almost works fro mmy Mac (12.5.1), but if Lightroom (5.5) ever decides the drive is "disconnected" for whatever reason, there's no way to fix it.
Using this basic configuration:
if I disconnect and reconnect, I end up in a permanent broken state telling me that volume is offline and to "Please reconnect to finish syncing." The volume is connected and, in fact, just hitting that Browse button and saving again will convince Lightroom to reuse the same path, but it'll begin by moving all of my photos into it (not entirely sure what this means, but it takes a very long time).
I'd assume, if nothing else, restarting Lightroom would see the path I have configured and begin using it again, but it seems to permanently fail if interrupted.