I have found that the GroupBy node in KAP 5.2.5 if you click on the Cancel button that changes done in the configuration still gets applied. When clicking on Cancel it should not save any unsaved changes in the node configuration.
I have not tested this in older versions of KAP so not sure if this is isolated to KAP 5.2.5 or not.
Further testing I found that it seems to not save the changes, but doesn’t update correctly when opening up again.
Create GroupBy, add 1 column in the "Group column(s) section.
Click on OK button.
Open configuration again and remove the column from the “Group column(s)” block.
Click on “Cancel” button.
Open Configuration again.
The column doesn’t show in the “Group column(s)” block, but if another column gets added, the original column will just appear in the "“Group column(s)” block.