Please download following performance test c# project here
Fill grid by Add and try to refresh data by Refresh Data or Timely Refresh Data
You can modify this sample to demonstrate incorrectness in FlyGrid.
Also, the screenshot shows sizing problem that I haven't gotten any response to yet. Last column is too slow compared to the others although all columns are set to AutoSize and FitMode.Spring
Perhaps this problem is also connected to the slow fetching in your project.
I saw timing example unfortunately but this example shows cells updating, not a fetching (getting values for displaying). We can provide you with debuggeable version of FlyGrid to measure timing on Node.GetCellValue/Column.GetValue methods on your project.