Good day. Child 1.5 years old. The regime is going off track. Earlie…

Good day. Child 1.5 years old. The regime is going off track. Earlier he went to sleep by 9 PM. Now it can be even at 12 o'clock in the night. He wakes up later in the morning accordingly. He also doesn't fall asleep during the day. There were no changes in time zones, everything was as usual. There were no changes in bedtime rituals and so on. Has anyone encountered such a thing? Maybe there is a crisis or regression? I don't know how to call this.