Most clematis are woody deciduous vines.  Their leaves die and fall each year and come back in the spring. Enjoy your plant and enjoy this excellent fact sheet from Clemson University in South Carolina.  They typically have more humidity and more disease problems than we do in drier Texas, but this is a very good source of clematis information. https://hgic.clemson.edu/factsheet/clematis/

Everyone can google.  I look for my favorite Extension resource to share.  Do you know the genus and species of your clematis?  What's is the microclimate like where it is planted?  How do you irrigate?  What's you soil type?   Does this happen at the same time every year or is it weather dependent?  How many years of growth records do you have?  Have you documented this with photographs?  

It's probably not a disease.  I was trying to say that disease isn't as often a problem in Texas as it is in South Carolina. 

It is possibly a normal dormancy.  When you are in Archie's, ask Steve McCoy if he has any experience with your clematis or if other customers have reported similar plant behavior.  

This vine may very well have frozen back to its roots this winter.