Once the delegates settled the Great compromise, what issue did they tackle next?

The Three-Fifths Compromise

Explanation:

Once the issue of the Great Compromise was settled, the legislators could continue their discussions on the composition of the legislature. The next problem that arose was the role of slaves, and how they would be counted when determining a state's total population for legislative representation. The compromise was to count three out of every five slaves as a person for this purpose. This is called the Three-Fifths Compromise.

The Great Compromise settled the method of representation in the legislative branch (the US Congress) ... Under the compromise, all states were represented equally in the Senate. This made the smaller states happy.