Thank you for the provided information and code snippet.
Custom templates are a known limitation for exporting to Excel. It is documented in this article:
"The Grid does not export its detail template to Excel. The reason for this behavior is that the detail template might contain arbitrary HTML which cannot be converted to Excel column values."
You can, however, use different data when exporting your grid to excel. A custom fetchData callback could be used for this purpose. A little more info and an example are present here.
In this example I have used a simple map function to displace the original value of the cell with a different, custom value.
Hope this helps - please do let me know if it does and/or if you require any further assistance on this issue.
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