I was just thinking to myself. If this is a yucca, say a soft-leaf variety or subtropical variety, then there would be a distinct point to the end of the leaf. I mean to say there would be a needle-like projection coming from the end of the leaf.
Since these pictures are poor, can you confirm if this 'thorn' or projection is at the end of the leaf? It should be about 3/4 inch long or longer and very hard and the tip will be like a needle.
Let us know,
Ron
If it is a subtropical Yucca, this might answer your question as to why it is failing. It requires much more light, direct light actually, so that the new leaves mature fully.