It is a preview of a report.
The first green box represents a table and the second green box represents the second table. I set the width of the table to be the same. In this case, it is 82%.
I drew a red line to indicate the second table is wider than the first table. Is there an option to force the text to fit to the width of the given column; so that, the second table's width is same as the width of the first one.
And you don't define widths on any columns and neither table is embedded in another element? Are you on fixed or auto layout? Can you reproduce the issue with the sample database and attach the report, so I can test?