Should this metric worry me (9% vacancy but under market rents)?

[Rob Simpson]

Has anyone experienced this, bought the property anyway, and have some wisdom to share?

This property I'm looking at boasts "huge upside potential" if rents are raised to the market; but, they're also showing a 9% vacancy cost in their rent rolls.  I've seen this on some other advertisements, and I question why a place would have nearly that much vacancy if they are below market rents.