19mo early wakeups

Struggling with early wake ups with our toddler. We keep getting into this cycle where we make a schedule change, it’ll work great for 1-2 weeks then he is back to waking up at 5:30am. Our latest change we pushed bedtime from 7:30pm to 8:00pm and it worked great. He was sleeping until 7am consistently which is more than we could’ve asked for. It’s suddenly fallen apart again and he’s woken up at 5:45 (or earlier) the last 3 nights. Nap time is consistent from 12-2. Bed time routine is the same. Room stays dark and appropriate temperature. When he wakes up we don’t engage or if we do very minimal until our desired wake up time of 6:30am. Looking for advice to try and get these early wake ups corrected. Thanks all!