This behavior cannot be reproduced at our end. Let us know if the problematic output results in the Report Designer's preview, in report viewer you use or when the report is exported in some of the formats.
If you view the report in web viewer, this issue might be caused by the differences in the way different browsers' layout engines interpret fonts and their sizes.
Test if changing the font family and size resolves the issue. Also, atatch some screenshots if possible that demonste the problematic output.
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