A lot of the issues first thing in the morning is about transition and making the switch from one thing to another. When they wake up from nap - first they are ready to take on whatever life is going to throw at them but more importantly they wake up neutral and more likely to accept what they see when they wake up.
It is also a sign of how much the child relies on mom to be their support and how self-reliant they are. Can they do anything without mom or not. Those that can will ease into the program much better after a nap.
It can actually work to simply take a screaming child on arrival and put them into bed and let them fuss themselves to sleep if only for a few minutes. Then mom is long gone and child emerges into the daycare with the caregiver at their side. It is a transfer of allegiance so to speak.
Glad your days are improving Lucy.