This issue can be reproduced by using the following code:
Razor<DxListBox Data="@mydata"
ShowCheckboxes="true"
SelectionMode="ListBoxSelectionMode.Multiple"
ListRenderMode="ListRenderMode.Virtual"></DxListBox>
@code {
private List<string> mydata = new List<string>() { "1", "2", "3", "4", "5", "6", "7", "8", "9", "10" };
}
The result is the following:
As a temporary workaround, add the following CSS rule to the page:
CSS.list-group-item {
border: none;
}