Looking at the description given above, if I got it correctly, then it seems you are getting additional blank page in the final output for one specific file? Do you get to experience this with all the files created using "Combine Files" feature?
You may try the following steps, and let us know the result-
1- If you are working on Document Cloud web interface, then use a different web browser and use the URL- Adobe Document Cloud
2- Check with different word and pdf file, try combining them and see the result. If same thing happen again, then-
3- You may share one of the sample file with us, as we would like to test the same at our end.
"You can share the file with us via email. And you can send it to the email address that is shared via private message. Please do mention your forum thread in the subject"