Has it ever flowered? You may have a sport of something that can be IDed. And if the flower is a dog, you could always disbud it & grow for foliage alone. If you do have an excess of long stems with this leaf coloration, could you please try layering some? I'd sure like to have a start of this.

Marie in ME

Photo?

My sweet autumn clematis has thrown stems with branches as you are describing from time to time. unfortunately the variegation is very unstable on my plant, it often disappears entirely by mid-summer as the growth continues and new leaves shade out the older ones.

~Chills

It could well be a SA. I have a huge one close by. I have to figure out how to post a picture. I know it's been described many times but I haven't paid attention as I wasn't posting.

SAC in my garden does the same thing in early spring. Once the weather warms up and stays that way the variegation disappears not to be seen again until the following spring.

The SAC in my yard, does that too.