The sub-report is replicated multiple times horizontally with different number of rows in its table item. Due to the different height of each row in the table the table rows' upper and lower bound will not match from one sub-report to another. This will cause the merged cells in Excel. Further information can be found in the Design Considerations for Excel Rendering help article.
You can make each row in the Table with the same height and test if this resolves the issue.
Regards,
Nasko
Telerik
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Feedback Portal and vote to affect the priority of the items