Can't defeat Formless One

You got stuck to a point where the dragon was suppose to jump back on high ground and do some AOE damage. Try to load last but one save and repeat the fight. The fight routine for dragon include some melee attack in case you get too close. To get to area where some chests are on display and from there attack the dragon with melee, forcing her to turn and reach to your approach. 

This is where the dragon is and the point where the health bar stops taking damage. From what I've seen of the walkthrough, it's supposed to spawn a barrier at some point and then return to lower ground, but it never progresses that far for me. Just an endless cycle of me attacking and zero damage being done. 

At that stage the dragon will spawn some low level undead (or darkspawn) and descent back in arena. Here's a fast battle (all settings to easiest mode) to see the stages. https://youtu.be/32Vj6beri_A

After 1:10, does the Dragon cast 3 lightning bolts? If not, get out from cover so she can shoot you (time your dodge to avoid damage).

No undead are spawning for me. The dragon cast her lightning bolts, but she won't budge from the perch or take any more damage. There's definitely some kind of bug preventing the fight from progressing, but no one else seems to have had this problem, so I'm stumped.

The exact same thing is happening with Fangscorcher too :/

The steps, for both dragons, are: 3 lightning bolts, charge from lightning storm, detonate a growing lighting bubble, come down as some small fry is spawn. Since there are 2 different dragons in 2 different locations I can only assume one script doesn't triggers. Try game repair. Also, I can test if your save is not corrupted. Upload a save before enter the fight with any of those dragons and I can test it if the battle can be done (yes, a corrupt character/save can alter the fight as well).

Just disable infinite mana and no cooldown if you play with trainer (Wemod etc)