There was mentioned error in this thread - Changing PageSize in DataGrid with bound Settings causes an infinite loop - about cycle after page size change. This problem is fixed but it doesn't work fully anyway.
If you have RadzenDataGrid with these setting
PageSizeOptions="[10, 20, 40, 60]"
@bind-Settings="@DataGridSettings"
settings is correctly set when you change PageSize.
Once you add default PageSize (PageSize="20"), you cannot change PageSize in PageSizeDropdown. It changes the value, then it goes one cycle (calling OnPageSizeChange etc.) and then it goes the cycle one more with the original PageSize - result is that the PageSize isn't changed.
When you somehow load the PageSize from DataGridSettings, you will see grid with correct PageSize. But if the default PageSize (PageSize="20") is set, the Page Size is changed to default when you change Page.
There's property PageSize, field pageSize and _PageSize - I was not able to debug it and find the problem