Both reporting, and querying whether others have experienced and/or know of fixes.
**SPOILERS**
The Final Assault attempt #1:
Reach all the way to the planar vortex, 2nd dark anchor's adds despawn as i approach and won't respawn... after going in and out of zone and logging a few times figure i have to abandon the quest. ~Hour lost. Couldn't find this bug elsewhere, nor a fix. Anyone else experienced it?
Attempt #2: No one else around in the zone this time, so things are much slower. Reach the vortex guardian, die, figure: why waste soulstones? It's always respawned me at the most recent 'step' of the quest anyways... respawn ALL the way back at the citadel wayshrine, all progress lost, all adds inbetween respawned. yay.
Not 100% this is a bug, but why have intermediary wayshrines, if at the final step you lose all the progress? I understand this is heading towards the end of the storyline, but not since i had a sega megadrive have I had to worry that if I die at some point I might lose multiple hours of progress...

Attempt #3: Lets wait and see what this
universal main story quest has in store next... I've read a number of other bugs exist in this quest too that i'm yet to have the joy of experiencing... never mind the fact that whichever companion you pick they tend to spend most of their time staring wistfully off into space while you die, and your 'team of friends' in the planar vortex just make you look like a wildly inconsistent multiboxer...
Please Lovely-Zeni-people... TES games are built upon the story. If you get ANY quests right, make it the central ones