Making text follow a curved line but it disappears

I am trying to make a text follow a curved path that I draw with the Curvature Pen tool, but when I try to move the text through the curve it starts to disappear in the path in some parts and finally I can't fit it in the center part so to say. In the picture below I wrote "THIS IS MY TEXT" as example, and when I tried to move the text through the line, the word TEXT was gone.