Date & Time: 2019/08/22 - around 10:05PM
Frequency: Once
World name: Zodiark
Character name: Leaping Bear
Monster name: Leviathan (Eden 3 Savage)
Party or solo: Full party
In-game time: 20:05 Server Time
Area and coordinates: E3S
Steps:
1. Engage the Stormy Horizon phase
2. A player gets disconnected during the Plunging Wave phase (?)
3. Everyone dies because a sudden Splashing Tsunami spawns right as a player get disconnected, killing everyone

Please see this Twitch Clip showing the presumed bug : https://clips.twitch.tv/RichCogentSaladTwitchRaid