I have been playing lol for two days and had this problem about ten times.
The problem is as time goes by the images (mobs, buildings, character) starts to go black and it becomes unberable because they seem like shadows i searched for various fixing methods but suddenly as this problem occured again while in game everything solved with the solution i found accidentaly.
When this starts to happen (it happened to me when i was dead and reborn by tracking my soul),
Press esc open system and at the first screen right on top of it there is "multisampling" which is the key word! change multisampling to any of those x2 x4 the problem solved
But because it slows the gameplay with slow computers change it again to x1 before u press esc again and close the screen if you want your computer to work smoothly. I did this change two times but i m quite sure it ll work with everyone with the same problem. Lastly i really think (the becoming black part) happenes because of your computer so i think no change of files of WoW will fix it.(IMO)
Just a tip for those angry players with this problem, please help this article to be shown by everyone so no one gets mad. Greetings from Turkiye. :)