At the constitution convention delegates from northern to southern states disagree about

Northern states and Southern states disagree about the Congress interference in slavery matters.

Explanation:

The Constitutional Convention was called " to render the constitution of the Federal Government adequate to the exigencies of the Union.", while Northern states were most abolitionists the Southern states still had slavery as main workforce and source of wealthy, but they did not pay taxes for it and did not want the Congress to end slaves trading. So many South states considered the slave as properties and wanted it to be protected and treated as such, while the North did not agree with that, as they saw slaves as person, so the delegates resolved this matter coming up with three-fifths clause, which would count slaves in the proportion of population for electing representatives and for matters of taxes.