What are the major issues affecting Africa? What is holding Africa back from achieving its potential? Where will Africa be in 25 years?

Africa can be divided into North Africa and sub-Saharan Africa. Some problems are common to both regions and some specific to one of the two. Both suffer from the legacy of colonialism, over-reliance on raw materials to drive their economies, high unemployment, tribalism, and various failures of governance. Sub-Saharan Africa is also particularly afflicted by epidemic diseases, especially HIV.
For North Africa, perhaps the country with the worst outlook is Libya. The overthrow of Colonel Muammar Gaddafi in October 2011 in Libya heralded a period known as the "Arab Spring" in which various states in North Africa saw movements demanding increased democracy and accountability from governments. While Tunisia has sustained a new model of democratic government, and Morocco and Saudi Arabia are gradually liberalizing despite having hereditary monarchies, Libya has descended into chaos, ruled by regional warlords and home to various radical Islamist groups and other insurgencies. Libya has fallen into a vicious circle where a lack of national unity and rule of law has impeded economic recovery, and especially oil exports. The lack of economic opportunity fuels lawlessness and extremism. If one group manages to dominate in the current power struggle, it may temporarily be able to address some of these issues, but unless rule of law, economic recovery, and a political system that can satisfy the interests of multiple factions and groups emerge, Libya is likely to remain a failed state for the foreseeable future.
South Africa has been one of the political and economic successes of Africa in the past several decades. It has a lively functioning democracy and free press, some strong educational institutions, and some innovative industries and businesses. Its progress has been impeded by HIV, widespread poverty, the legacy of apartheid, high unemployment, and political corruption under the leadership of Jacob Zuma. With Zuma's replacement as leader of the ANC by Cyril Ramaphosa in 2018, there is every reason to be optimistic about a return to economic growth. While economic growth, labor market reforms, and better governance will not happen instantly, there is every reason to be optimistic about the country's progress.
https://www.bbc.com/news/world-africa-24472322