Begin editing the first cell firs column
Without closing the cell editor, scroll down to the last cell, the first cell should exit the viewport.
Start editing the last cell.
Scroll back up to the first cell

The content inside the first cell is missing.

The content should be there.

Keep the data grouped, make the window a bit smaller so you have a decent amount of rows to scroll through, and using your mouse wheel, scroll up and down quickly. Eventually you'll notice that the grid will start to bounce a bit. For example, you'll scroll down and then without scrolling the mouse wheel up at all, it'll jump back up a few rows on its own.

Starting with v10, all groups except the last, get a blank, empty row.

If you toggle off the grouping, the empty rows go away, but once you put the grouping on, these empty rows show up again.

Some data is missing from the UI when grouping is applied and then filter the data. 

If you ungroup, the items are displayed.