Steps to reproduce:

1. Set the time to midnight.
2. Summon a large amount of creakings by placing creaking hearts between pale oak logs.
3. Give them the Infested effect.
4. Break the creaking hearts.
5. No silverfish spawn despite the creakings having the Infested effect. This effect still counts instantly killing mobs as damaging them (tested with husks and /kill), therefore the creaking should also have a chance of spawning silverfish.