Based on the provided screenshots, it seems like this behavior in Excel might be caused by misalignment of TextBoxes. Test arranging the TextBoxes so the left and right/ bottom and top edges of all report items line up with one another.
The GroupFooter section will also take place in the rendered document. You can hide this section with Visible=False
Other specifics of Excel rendering extension are described in Design Considerations for Excel Rendering
In case, the issue persists please attach a sample report in a support ticket so we can check the settings and give you further suggestions.
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