Command block minecarts do not execute every tick but instead every 4 ticks. However, their cooldown is not saved to NBT. This means when a world with a command block minecart which is supposed to execute the next tick is closed, it will execute after 4 ticks again after the world is reopened.
- Summon a command block minecart
- Inspect its NBT data
→ There is no tag tracking the execution cooldown