plot hole

US /ˈplɑːt hoʊl/
UK /ˈplɑːt hoʊl/
"plot hole" picture
1.

a gap or inconsistency in a story's plot that goes against the flow of logic established by the story's own rules

:
Fans pointed out a major plot hole in the movie's ending.
The detective's sudden appearance without explanation was a clear plot hole.