Is it necessary to stop striving for a master's degree after repeated obstacles, or is that a test from Allah?

There is no standard answer as to when a person should stop striving. The correct path might be to stop or to continue. To determine this, one should list the opportunities, alternatives, and risks, then consult with people of knowledge and experience. And know that all affairs of a believer are good; if ease befalls him, he is grateful, and that is good for him; and if hardship befalls him, he is patient, and that is good for him. Seek help through the Istikhara prayer, frequent prayers upon the Prophet, and supplication, and through your good relationships with people.