Yes, it is possible for a buyer’s mortgage to be denied after preapproval. This could happen because of an issue with the appraisal or guideline changes made by the lender.
But in most cases, getting denied is due to the buyer’s financial standing being negatively impacted such as with a change of employment, a decrease in credit score or accrued debt. It’s important to not make any mistakes or drastic changes until after closing on your home.