I have found an odd behavior in the grid when group and filterBar features are enabled and selectionMode is configured to allow all rows selection.
In summary if the store if filtered and a group of rows is collapsed, select all rows do not select these “hidden” rows. The same does not happen if the store is not filtered.
I have recreated the issue in this modified live demo https://codepen.io/javicloud/pen/yLXOXax?editors=0010 created from the one https://www.bryntum.com/docs/grid/#Grid/feature/Group
Attached you can find video recreating the issue.