We went thru the same situation. My mom applied for the visitor visa after us embassy took her GC for staying long time in Nepal. They took the passport on the interview day for visa granted and stamp. She got a call next day to come to the embassy and asked about staying long time in Nepal holding a GC. My mom has multiple health conditions including she is the breast cancer surviver which she explained to the consular but they rejected her visitor visa next day. We were shocked. Good luck to your father. My mom's case is in national visa center now after I 130 approved.