The source code does not follow desired style or formatting for indentation, white space, comments, etc.
Variations in indentation and other white space, comments, etc. can make it more difficult for human analysts to understand the actual behavior that is being implemented.
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)