Happens to me all the time.
It’s due in part to your hair not being processed completely. Upon first relaxing, and rinsing out the relaxer, those ionic deposits from the relaxer don’t get rinsed out completely. Over time, usually about a week or two, they will completely rinse off. Ionic metal compounds in relaxers tend to coat the hair. Usually making it stiff, heavy, and more or less weighed down. That’s not to say some curl pattern isn’t still there. Typically it won’t show itself until most of the residue is done, and that texture has a chance to come through without the deposits weighing the curl pattern down.
This happens to me almost every relaxer, and I often times mistake certain parts of my hair for new growth, when it’s actually hair that’s been relaxed, but not processed completely.
It’s not really a bad thing, and I just let that part of my hair be, since it gets fully straightened out during my next application from a bit of overlap.
Your ends however, will not revert. With them being older, and more or less porous than any other part of your hair, upon relaxing them, they are mostly devoid of any texture.
I wouldn’t worry about the under processed parts unless it’s causing breakage. But it’s normal. It’s not that the relaxed hair is reverting, it’s just that your new growth, combined with any hair that wasn’t fully processed is now showing itself.
