You can argue that the Berlin Conference is still causing problems in Africa because that conference split the continent up into countries without any rhyme or reason and because it gave those countries to various European powers to rule for their own benefit, and not for the benefit of the natives.
Countries seem to work best when their people have something to hold them together. This is often a shared language, ethnicity, and/or history. The African countries that were created by the Berlin Conference lacked these things at the time and they generally lack them today. Instead of being made up of people with something in common, they were made up on the whims of Europeans. This means that today’s African countries are full of various ethnic groups who do not necessarily get along with one another. The more horrific evidence of the problems this causes was the genocide in Rwanda in the 1990s, which was caused by ethnic tensions. While this was the worst problem caused by the drawing of boundaries at the Berlin Conference, there have been many others. The tensions between the various ethnic groups within countries makes it so that those countries are not united and it often makes their governments as each ethnic group seeks power simply to improve its own lot, not to help the country as a whole.
In addition to creating these ill-conceived countries, the Berlin Conference gave those countries to Europeans to run. The Europeans ran the countries entirely for their own good, not that of the natives. This means that they created economies that extracted resources from Africa to help Europe. It means that they trained Africans only to do relatively menial work. It means that they did not give Africans any role in governing themselves. When the Europeans were forced to leave Africa in the wave of decolonization in the 1960s, they left behind countries with poorly developed economies and with populaces that were not trained or prepared to run modern economies or governments. These problems persist today. Thus, the Berlin Conference created tremendous problems that continue to make it difficult for African countries to prosper today.