I just had this problem start. Curves ADJ was there a few minutes ago, now it isn't. The only thing I can think of that may be related is that I use ALT+RClick on the ADJ layer icon on the Layers palette all the time, and I think I may have dragged the cursor.
I just found this weird bug right now. Is there some workaround to have the Curves adjustment layer back on the menu? Resetting my preferences is not a desirable solution at this point, but if it's the only option I'll give it a try.
I also get this problem randomly. The only way to fix it, AFAIK, is restarting photoshop. Since it happens every once in a while, it's hard to say if it's totally random or related to something else (using a plugin or who knows what).
I'm on Windows 8.1, PS CC 2014.2.2.