Your combos will also not work if one of your ninjas, that's supposed to chase, gets paralyzed, immobilized, etc - that will break the entire combo altogether.

The positioning of your ninjas will also affect who will carry out the combo first/next so make sure you position your ninjas in the order that you want so you can fire off your combos correctly.

It seems like you're Pakkun is interrupting the combo. Use another summon or take him out to see if that is the case.