Do you still have this problem, Samuel?
If so, can you hack up a small data set and upload a sample workbook?
Follow the steps in the video linked here:
The thrust behind that video is to show how to anonymize, but if you don't need to anonymize anything just do it to get a 100-row sample set. (Make sure some of the problem rows are included in there.) Really, all the rest of your columns won't matter here. Just the columns you are concatenating, and one bogus measure would do.
This sounds like an aggregation issue where the workbook is showing the aggregated value vs your data source on Tableau Server showing you every row. Did you figure out the issue or are you still experiencing problems?
This is something a Tableau Support engineer could confirm with you in a remote assistance screen share if you submit a case to https://support.tableau.com