United States Grain Standards Reauthorization Act of 2020 This bill reauthorizes through FY2025 the United States Grain Standards Act, which authorizes the Department of Agriculture (USDA) to establish official marketing standards for grains, and to provide procedures for grain inspection and weighing. Additionally, the bill requires a state agency to notify customers or applicants for weighing or inspection services if it intends to temporarily discontinue the services; extends the authority of USDA to collect fees to fund official inspections and provide official weighing services through FY2025; extends the cap on the administrative and supervisory costs through FY2025; requires USDA to publish quarterly reports describing data from the tests and inspections for intrinsic quality factors (including protein, oil, and starch) and food safety factors; requires USDA to publish quarterly reports including the number of certain waivers and exceptions that were requested and granted; prohibits the use of user fees for activities related to the development or maintenance of grain standards, or for any activity that is not directly related to the performance of an official inspection or weighing service; provides that members of the advisory committee with respect to the act may serve up to two consecutive terms and extends the authorization of the committee through FY2025; and requires USDA to conduct a comprehensive nationwide review of the official agency geographical areas.