Injection of Glucagon is effective for management of persistent hypoglycemia in all EXCEPT –
Large for date baby
Galactosemia
Infant of diabetic mother
Nesidioblastosis
Hypoglycemia in hyperinsulinmic state require IM glucagon as treatment.
Glucagon increases glucose level in blood by Glycogenolysis and Gluconeogenesis.
But in galactosemia - Liver is the first organ to be affected, so glucagon will unable to increase glucose as glycogenolysis and gluconeogensis can not occur ion already damaged liver.

Nesidioblastosis :

It is persistent hyperinsulinemic hypoglycemia occurs due to 0 - cell hypertrophy in infant of diabetic mother due to continuous maternal hyperglycemia.
Glucagon is effective in controlling such a hypoglycemic condition.