Temple of Kopec Alva bug

I was playing coop with a friend. After killing the boss in Temple of Kopec, my friend interact with Alva there and the platform move him up. I was not on the platform and stuck, when I teleported to him, the gate did not open and the quest objective still say travel to Temple of Kopec. When I traveled to Temple of Kopec, the objective is talking to Alva, but the NPC is not there anymore and there's a barrier around the middle circle. Questwise, I stuck here.

any solution? having this exact same issue

Here with the same exact issue.

EDIT: There is a temporary fix:
1.Possibly** Leave party.
2.Respawn at checkpoint.
3.Run up and Alva should be there. The boss lines and orbs will be flying but he won't be there to fight.

Reset the map work for me

Nothing is working for me, I have just defeated this boss 4 times in a row and still can't complete

Had the same issue just now. My friend rode up the elevator and I was left unable to progress.