In 2.4.0 update (released on 6th of February) the unlocking frequency of the Hatchlings was evened out. As we did not want to re-lock Hatchlings that had been already collected, there can now be one longer gap until the next Hatchling gets unlocked.
Example: You were at level 195, your latest unlocked Hatchling was Madison from Faking History. In the new update Madison will only unlock at level 240. As you have already unlocked her, you will unlock your next Hatchling at level 260.