Exporting to excel is merging columns for SSRS Report

This issue usually occurs when alignment and dimensions of column for a particular cell is not properly defined. There can be two scenarios:

Dimensions Issues: column and rows of a particular cell should be defined with whole number. In SSRS, click on a cell and go to properties and set width and length to whole number up to two decimals.

If on the report before your table, some text boxes are defined then also it will hinder the export of report into excel. In order to resolve it, you should create an empty table at the very top of report. This table should be hidden. All subsequent tables should be aligning with top tables. Report gets rendered from top to bottom, if we set the top header as fixed it will help to render the report in proper manner.