As the real estate market softens, Opendoor's bottom line appears to be following suit.

The iBuying giant is for the first time selling homes at a loss. Analyst Mike DelPrete said in a research note it's the result of a fast-changing market, cooled by rising mortgage rates and stock market uncertainty.

Those factors have combined to hurt home values at a time when Opendoor is on the hook for properties it picked up in a historically hot market. A Bloomberg analysis of Yipitdata says that as a result, the company lost money on 42 percent of its sales in August.

"Opendoor doesn't necessarily have a crystal ball to see into the future with 100 percent accuracy," DelPrete said. "A lot can change in a couple months."