Possible Reasons an I-94 Stay Period Is Shorter Than Six Months When Entering the U.S. on a B Visa
This article outlines several situations in which the I-94 stay period may be shorter than six months when entering the United States on a B1/B2 visa, including overly frequent trips, a handwritten error in the admission stamp date, and a passport valid for less than one year. It also notes that mainland China is not on the Six-Month Club list and that the I-94 website date controls.