Problems with the fight in order of appearance:
Wrong number of people teleported.
Killed by architects upon teleport.
[Hard] Detained when teleported.
[Hard] Detain is the same size as titan shield. If you bubble, then get detained, you can't shoot detain from the inside or outside.
[Hard] Detain debuff is permanent.
Enemies spawn behind you inside portal.
Minotaur heals to full.
All oracles spawn at once.
Oracles spawn invisible.
Succumb to oracles after they all died.
Vengeance does not pop on the last oracle.
Gate doesn't teleport.
On kill effects not activated upon killing supplicants.
Splash damage goes through cleanse shield.
Projectiles go through cleanse shield if the relic bearer is nudged.
Atheon walks out of LoS and stays there, wasting a whole phase. Not a bug, but I'm posting problems, not bugs. In hard mode, you can't survive outside the bubble easily at 29. Repositioning can wipe the whole raid.
Atheon's critbox is ambiguous.
Atheon stomps on the center.
Certain weapon perks stop working after vengeance.