It can be reproduced easily.

1. Make Window, layout: 'fit'
2. Make Grid panel inside window as a child.
3. Set a 'locked: true' one of the columns.
4. Resize window

then you can see vertical scroll jumps to the top.

Below is my example fiddle for this bug.

and there is another bug.

if you're doing this process(resize and scrolling) repeatedly, you can see some empty records.
In Grid panel, there are some blank records view.

I think it's a critical bug, but it's still not fixed.

It's basic and simple function for grid.
I hope it's fixed as soon as possible.