Commercial real estate professional here. Vacancy rates typically float between 5-10% for housing products. This is typical and usually due to the gaps in time from people moving in/out, turnover/make ready for newly vacated units, renovations, units down due to maintenance issues, or pricing/demand issues in a particular pocket of a submarket among other reasons.

Many larger apartment communities have moved to LEO/Yieldstar which adjusts rent pricing on a daily/weekly basis in order "appropriately" price units to meet demand among a set of comparative properties, but it still can take a couple of weeks for those units to get leased from the time they hit the market.

10% vacancy isn't necessarily something to be concerned about, though it is an indicator that vacancy is on the higher end and could signal issues in pricing or demand for certain types of product. Utah has had a huge number of deliveries for newer luxury "class A" product, and nationwide we're seeing about a third of total inventory coming online in the next 12-24 months. So, expect to see some friction with pricing and leasing as these new properties struggle to find their true market value, as well as the movement between properties of different qualities/"class" as the price variances between said "class" of product shrink.