Hi Victor,
From the provided information it seems that the issue comes from having duplicated element ID attributes on the page - by default the DropDownList editor for the ForeignKeyColumn generate it's ID attribute from the current model property name. Possible solution is to generate unique IDs based on parent Grid model ID using custom editor template for the nested Grid - please check the example below:
customFKCEditor.cshtml:
Regards,
Vladimir Iliev
Telerik
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