There’s a bug with Version 1.5.2 of Xenoblade Chronicles 2, but there’s a workaround
Nintendo’s Japanese website states that the latest update to Xenoblade Chronicles 2 added an annoying bug to the game, causing some quests impossible to complete in certain cases. Perfectly Nintendo lists the Blade Questions with problems:
Flames of Justice (Godfrey’s Blade Quest)
Failure and Success (Perceval’s Blade Quest)
Lost Kingdom (Daga’s Blade Quest)
Blade-Sharp Memory (Praxis’ Blade Quest), along with Pest Control 3 (a related quest that’s part of this Blade Quest)
Eternal Spirit (Perun’s Blade Quest)
Limits of Awareness (Adenine’s Blade Quest)
A Real Challenge (Zenobia’s Blade Quest)
Nature Boy (Floren’s Blade Quest), along with Unspoken Suspicion (related quest)
The Calm and the Storm (Herald’s Blade Quest)
To get around the issue you need to only use Auto Attacks or Individual Arts as your finishing moves. Tetsuya Takahashi from Monolith Soft. said a fix will be in Version 2.0, which will be released along with Torna ~ The Golden Country on September 14.