In the attached sample, the grid ColumnDefinition is defined as 0.5* for 2 columns and in each column, an SfDataGrid is placed. When the sample is run, each SfDataGrid must take 50% of the SfAccordionItem's width but it takes the width to fit the first placed SfDataGrid which is 50% more the width of the SfAccordionItem thereby not considering the 0.5* width defined for the column.. This issue occurs even when the SfDataGrid is replaced with MS DataGrid or even with the TextBox.
The same template applies correctly when SfAccordion is replaced with the GroupBar.
1. Run the sample.
Note that the first SfDataGird occupies more than the 50% width.