Hi! Did you already find a solution for this? I would be interested in more threads about repeater and AJAX. But to the point, I found this to work with repeater subfields.
// where field_609b103fcd576 is a sub-field in my repeater
acf.addAction("new_field/key=field_609b103fcd576", function ($field) {
$field.on("change", function (e) {
var value = $field.val();
console.log(value);
});
});
When tested on new or not-the-first repeater row this gave the correct value for each sub-field.