Perhaps he avoided the effects of the curse because he had no happily ever after to be destroyed on FTL. If you think about it, all we know about Rumple are sad things. He lost his wife, his son, and Belle. He became a monster, something I feel he regrets, though he loves his power. Perhaps his suffering is remembering everything in his past – if he hadnt, his life in Sb would be far better (it seems) than his one in FTL. In SB he has a high place in society and is feared by many. In FTL he lost everything that meant something to him. If the curse had black out Rumple like it had everyone else, he would have been happier than he was in FTL. Perhaps the curse did work on Rumple, but rather than blacking him out so he could never be happy, he remembered so he could never be happy. Isn’t that the real point of the curse, to never have a happily ever after.