Two tablespoons of filling per pancake, no more. Overfilling is the commonest reason they split in the pan, and a krokiet that has burst leaks its filling into the oil.
Let them stand a few minutes before frying. Going straight from a cold fridge into hot oil is the other main cause of splitting. Keep the pan at a medium heat rather than a fierce one.
Freezing. Best frozen rolled but not yet breaded: freeze them on a tray so they are not touching, bag them once firm, then thaw in the fridge and bread and fry. They also freeze fried, and reheat from frozen in a hot oven at about 190°C for 15 to 20 minutes. Either way they keep around three months. Do not use the microwave, which softens the coating.
The filling can be made two or three days ahead and kept covered in the fridge.