Having similar issues , playing vanilla on stadia. First time I killed the whole grove , so not sure what's supposed to happen but Minthara keeps saying to me that I have to hunt down more thieflings when standing in the small room with the map while I am pretty sure I killed them all. I think it might be because I used the shortcut via the druid library and start killing them 'from the inside out' before joining the goblin army at the gates. Quite frustrating and considering a restart because of not knowing if I broke my playthrough yes or no.
