What issue was addressed by the 3/5 compromise?

It was to give Southern states more seats in Congress and more electoral votes if the slaves were or had been ignored.

The Three-Fifths Compromise was a compromise reached among state delegates during the 1787 United States Constitutional Convention. Whether and, if so, how slaves would be counted when determining a state's total population for legislative representation and taxing purposes was important, as this population number would then be used to determine the number of seats that the state would have in the United States House of Representatives for the next ten years. The compromise solution was to count three out of every five slaves as people for this purpose. Its effect was to give the Southern states a third more seats in Congress and a third more electoral votes than if slaves had been ignored, but fewer than if slaves and free people had been counted equally. The compromise was proposed by delegate James Wilson and seconded by Charles Pinckney on June 11, 1787.