I believe IRCC's method is that the estimated time in months means that 80% of apps (i.e. 'most') are done within that time frame. That leaves the 20% that are by construction deemed 'complex', i.e. those 20% are those that are taking longer than usual - most of those probably do have some substantive issue, and a few (inevitably) just had some random processing issue .
Of course that means that quite a lot are completed in shorter timeframes than 7 months, i.e.
@moman21 said "a standard application can be 3 to 5 months" and that's probably also a reasonable statement.
It's an estimate, it's backward looking, and other usual caveats.