During the Sortie, it may happen that the Infested Corpus part of Lephantis will bug during the first stage of the boss, and he will not open his mouth at any moment after getting out of the ground, going back underground with no windows to damage him. This repeats multiple times, till it finally decides to open it's mouth after a long time. This happens only in the first part of the battle, and the host doesn't seen to matter for this.
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Moderator Edit:
This is a known issue and DE are investigating:
