Currently the scenario is bugged and teleports me back to base after the second wave of attackers.
Edit: seems that you hit an invisible wall or something right past the mine which teleports you back.
Edit 2: I was able to clear it without bugging by going full burst spec, with hero/lust, and killing all the add waves before the bugged spot.
Yup, still bugged after reset. Get warpped to camp during start fight in the skies. Seems there is a barrier that is either too small or not working correctly causing it to act as out of bounds or left the area, making it impossible to do the Isle of Thunder Campaign achievement or the ability to unlock dailies for Sunreavers.
Same thing happening for me, and for the crowd of people gathered at this scenario right now. There’s an out of bounds region or something, it’s impossible to do the Isle of Thunder campaign until this scenario is fixed.
same thing for. also found multiple other player with same issue in general chat.
Thank you for the second edit. It worked for me with enough damage you can bypass the tele.
yea I’m having that issue to its literally not doable I’ve tried maybe 10 times and can’t do it blizzard has to fix it
If you kill the birds fast enough you can get past that part, then you get stuck in the mine because that part is bugged also when the npc will not open the door
Some finicky cheese until a fix: You can avoid the teleport if you spam hop to other pterodactyls, but the last one will drop you in the sea/by the rocks beneath the mine. Stick Door of Shadows or something on your boots and you can climb back to where your boy is meant to drop you, but he’ll just be hovering way up in the air and the next phase won’t have triggered. Abuse more movement to climb the nearby rocks and get near enough to him; he’ll despawn and the boss will spawn. Taoshi RNG was kind to me and I had no further problems with the mine.
blizzard are incompetent this same bug has existed for years with no fix yet , then you have the former lead dev asking for tips …hell no !!!
This is a MAJOR bug for this event! Grrr…
Come on Blizzard, new game mode and it’s bugged to hell and back. Good job! 
Please fix this ASAP
Just ran in to this issue this morning. Rather frustrating when mogs are locked behind a near impossible achievement due to this.
as per OP’s edit, it worked as a getaround for me. Used the buffs from scrolls, and my cd’s and lust and killed all the flying mobs before the bugged part, I was then able to complete the rest of the quest
I managed to kill them all as a mistweaver using lifestorm, all dmg tinkers, every scroll type and no lust since I was sated. Saved lifestorm and touch of death for the final set of 3. Hopefully this gets fixed soon.
How? The instant I engage with the first mob, my extra action button vanishes. I even disabled all addons, cleared my WTF folder, and I still love the extra action button as soon as I’m in combat. Once I kill each mob, I’m auto-ported to the next pterodactyl, but I still can’t kill them all in time.
I see another bug that’s never been fixed. Not sure how to get around this one, had to leave 7 times so far.
I managed to get this done as well, by doing as someone suggested previously, full burst spec, and when you get to the triple dragon, use Lifestorm meta gem and pop off. Scenario completed with no bugs further on. (post as wrong toon previously, annoyed me lol - repost of reply)
Seems to be near impossible as an arms warrior, at lvl 70 with the terrible scaling it’s impossible for me to kill the three riders before being teleported back to the quest hub.
Edit: I chose to kill 3 rares to get the achieve done instead. I recommend this option, or the option of doing all the queuable content for those who struggle dps wise.
Unable to complete this scenario today. Phase 2 is bugged and teleports you back to the outpost after about 20 seconds of fighting the flying attackers.
Using all buffs, tinkers and burst abilities as a shadow priest isn’t enough, I would need to get extremely lucky with crits of damage for everything to die in time.