I’m not sure it is technically a bug but I guess it’s not really an intended feature. It did not occur since long, so I thought it was already fixed.
Today I reached Lagon and when I stepped on the platform he closed it with his tentacles. Trouble is that my minions were a bit behind me and the access was shut just before they arrived. Therefore, when the fight started I was alone on the platform.
BTW, I did not understand what the problem was so I went to them in order to see. And I did not see Lagon was channelling his beam. I died. I was deathless. 