That's an odd one. I'd say the quest to investigate Kaugha didn't complete properly for some reason
My usual way to do this area - warning lots of spoilers
go in the grove, chat to everyone talk my way down into the inner grove to help the kid
Get into the inner grove save the kid and talk to everyone
Sneak my way back to that chest with the note to get the investigate Kaugha quest. Chat to Kaugha but back out of finishing the conversation - literally as soon as she's said a few things I just back away and cut off the conversation.
then immediately go do the investigation part over in the sunlit wetlands - with a passing stop to deal with the goblins and their druid captive in the cave underneath the grove that you reach on the right after exiting the grove, the owl bear mamma and tell Scratch to follow my scent etc and do it without triggering anything else by swinging hard left off the path and wading through some trapped water towards the bloody campsite as soon as past the 2 lads arguing with the old woman - whatever you say to the lads make sure you have the save Mayrina bit in your log afterwards, even if they refused help - but ignore it totally for now.
The bloody campsite is handy for looting food and sellables early game and then follow down keeping to the left at all times to the jump over to the little rocks from the small jetty and then to the tree.
Go do that bit and grab the note from the tree.
Head straight back to the grove and confront Kaugha in the inner grove. Give the note you found to Rath when prompted by the Shadow Druid. Talk Kaugha into betraying the shadow druids -that bit is easy - several ways to do it, she will join the fight against the shadow druids on your side.
After that just wait and stay in earshot.
Kaugha and Rath will have a chat and she will be repentant and you can then talk to her and she will rescind the rite and everything.
Chat to Zevlor is his little hideaway to get a reward for stopping the rite.
At that point you have all the time in the world to do the rest of the area and all the druids and tieflings are friendly. I pop in and out at will and trade . Up till now I have done everything without recruiting Wyll as I don't need him for anything
Personally I do everything else now alongside a few long rests including the save Mayrina one that hasn't triggered past its initial quest mention because of how I got to the tree, the Zhent including going down the elevator in their cave and looting like crazy down there, save whatshisname from the fire in Waukeens rest and get councillor Florrick out and complete all their chat bits and pieces - deal with Wylls quest and recruit Karlach. Head to the abandoned village, Free Barcus and drop down the well to kill the spider matriach and also because the forge in the village there has infernal metal for Karlach, then we go do her first fix. Hard save, Long rest get the Mizora scene. Then head to the goblin camp and kill all the exterior ones to free up the cub and Volo. There is no communication between interior and exterior so at this point nothing is set in stone if you want to do anything else. I usually have a long rest again at this point. Next for me is to go in through the roof entry and stay on the rafters to kill all the goblin leaders first then jump down to smack Minthara (or kill depending on my mood ) . I sometimes kill all the goblins sometimes I don't but I don't go anywhere near Halsin, once the leaders are dealt with he deals with his own extraction. Then I go down the long ladder to get the waypoint in the Selunite Outpost.
When I go back to the grove after this I enter via the cave not the main entrance (where you found a couple of goblins with a druid prisoner initially), which leads me out into the actual inner grove and avoids speaking to anyone, I find Halsin back in the grove and berating Kaugha - outside the inner shrine door or near the bottom of the exterior steps - who is suitably repentant and then wanders off to do guard duty or whatever it is she's doing. Chat to Halsin who will 'see me tomorrow', chat to Rath to get the reward, go chat to the Zevlor and get his thanks and start the party. Even after this I can still pop back to trade with Aaron right up to going into the Shadowfell - even though I usually don't need to, Kaugha is usually standing on the rim overlooking the shrine as a guard but has nothing to say.
