These are the possible causes of seizures in a puppy:
LESS THAN 1 YEAR OF AGE
Anomaly: hydrocephalus.
Inflammatory:
Infectious - Viral: canine distemper; parasitic; bacterial; fungal
Immune mediated
Metabolic:
Hepatic - portosystemic shunt; Autoimmune thyroiditis (early stage: TgAA
positive); Hypoglycemia; Electrolyte disorders
Toxic: Single or combination vaccines; Lead; Drug related; Other exposures
Trauma: Acute; Delayed
Degenerative: Storage disorders
Primary: Idiopathic Epilepsy ("idiopathic" = cause unknown or undetermined) POSSIBLE CAUSES OF SEIZURES BY AGE
Has your puppy had a bile acids test? If it's not hypoglycemia, that's the next thing I'd suspect.