I just did this again on my Warlock last night and there was no blockage to the stairs on phase 1 or 3 of the fight. I noticed when I misfired my Transplant and ended up on the stairs. I was so focused on the fact the stairs weren’t blocked in phase 3 I don’t even remember if there were waves. I had to get to bed so the thought of reporting it didn’t cross my mind.
Not sure about this but there is definitely an exploit for Lagon that needs fixed where certain builds do not need to engage him properly and can stand at the side somewhere (never tried it so not sure where, anyone know?) and kill him without ay danger.
I was definitely in the monolith version of the fight when the bugs happened.
I’ve also noticed that even when the tentacles are blocking the stairs, you can stand right in the corner, right by either one of them, and neither lightning attack (The blast, or the sweep) will hit you. I’m pretty sure that wasn’t the case pre 1.0.
If you are a ranged character, and have either some ward or leech, you can basically just stand there and tank the boss, with what few attacks can reach you.