Came to say the same thing -- looks like the "initial problem" (outermost group) was solved but expanding any sub-groups by default is still an issue.
I'd also add that ideally we can do this programatically and not just in the UI of the table. It could be something added to the Eventhandler UI when choosing the 'Set Grouping' option -- or just allow something like an expandGroup option when setting that grouping:
{ columnId: string, sortDirection: 'asc' | 'desc', expandGroup: true | false}
+1 to letting me know when it's solved.
Is there a programmatic workaround in the meantime?