REJECTION is not the same as DENIAL! Rejection is for a minor thing like forgetting to sign it or including the wrong filing fee amount or forgetting to sign or enclose your check. DENIAL is for cause. Denial for ALL visa petitions is solely for failing to satisfy the statutory REQUIREMENTS. The requirements for an I-526 is showing sufficient clean investment funds and having a pulse. USCIS will disagree on the "pulse" and substitute the "comprehensive,detailed, and credible plan for creating the required number of jobs". IF affiliated with a Regional Center, the alien investor just needs to show the source and path of sufficient lawful funds. I-526 approval does not guarantee a VISA or Adjustment of Status (Green-card). Just like any other intending immigrant you must be admissible under the Immigration and Nationality Act (INA Sec. 212(a) and some people may need a waiver for some reason--an arrest or prior immigration violation is most common or even a communicable disease--that can be OK if you agree to, and comply with, treatment).
The investor is unable to properly trace or show the source or the investment.
Having outstanding public charges in the United States. For example if you travelled to the United States in the past and used but did not pay for emergency hospital charges.
The issues that cause the most rejections for an EB-5 visa application are source of funds documentation and investment job creation issues.