Hey,
This is a known issue and Bungie are investigating it.
[quote]The Season 15 Pathfinder and Season 14 Lightkin armor sets are no longer available to equip as ornaments if previously unlocked via Armor Synthesis.[/quote]
Via the [url=https://help.bungie.net/hc/en-us/articles/4416375175444]Current Known Issues[/url] article.
Keep an eye on the [url=http://www.bungie.net/en/news]TWAB[/url] and [url=https://twitter.com/BungieHelp?ref_src=twsrc%5Egoogle%7Ctwcamp%5Eserp%7Ctwgr%5Eauthor]Bungie Help Twitter[/url] for updates on the issue.