Final answer:
The Fatui diplomats were staying at the Goth Grand Hotel during the Stormterror issue in Mondstadt, which is part of the game Genshin Impact.
Step-by-step explanation:
The hotel where the Fatui diplomats were staying during Mondstadt's Stormterror issue is Goth Grand Hotel. This location is a part of the storyline in the popular action role-playing game Genshin Impact, developed by miHoYo. Players encounter various characters and groups, including the Fatui, an organization with diplomatic ties but often sinister motives. Throughout the game's quests, the player learns about the Fatui's involvement in Mondstadt and their occupation of the Goth Grand Hotel during the Stormterror crisis.