A developer in your team used a custom form control but found that the valueChanges observable isn't emitting values when the control's value changes. What might be the potential reason and how would you resolve it?

The potential reason for the valueChanges observable not emitting values when the custom form control's value changes could be that the custom form control is missing the FormControlName directive in the template. This directive binds the control to the form and allows it to propagate changes. Options a and b are not the typical reasons for this issue, and option c is unlikely unless there are other symptoms of a deprecated version. It's crucial to ensure that the custom form control is correctly integrated into the Angular form template.