Failing interview for wireless Modem Systems profile again and again

Hello, I have a Masters degree in wireless communication with several years of experience. However, I keep failing interviews over and over for Modem systems engineering. Due to my current nature of work, I only qualify for systems and modeling positions and I get calls mostly from systems positions. These are my interview summary: Onsite 1: Marvell for position of system modeling: Around average. Couldn't solve few questions of probability. Accuracy around 70 %. Reject. Onsite 2: Qualcomm Modem systems engineer: Was quite decent and able to answer most questions and solve the probability questions correctly. Accuracy was around 80 % and thought my chances to be 50-50. Reject. Onsite 3: interview for modem system engineer at a small RFID company. Interview went really well. After 4 days, they asked me to complete an information form. My references told they were contacted. They didnt give me decision till Jan 2nd week (2019). Reject. Onsite 4: Interview with Qualcomm modem systems team in December 3rd week. Interview went really well and was able to solve and answer everything. Manager showed around office and labs. No result till now. HR was unresponsive and after I called manager recently, HR sent email immediately that there has been no decision yet. I dont know what to do. Last 2 interviews were impeccable and dont know what else can I do. Is my Masters hurting my chances for systems role? I am really broken. Thanks