There’s a delay every time some is at my door, or even on the motion sensor. By the time it reaches my phone there is no one there , they are already down the road
Sounds like delivery people. Most of the people that deliver stuff to my door never bother to ring the doorbell or knock. They are barely in my yard 20 seconds before they are gone.
On your phone do you use a Do Not Disturb or Sleep mode? I do, and I notice that notifications can be minutes after the fact.
Do you have the Frequency and Sensitivity settings at max for your doorbell? Be aware, if you doordell uses battery those settings can eat into the life of the charge on the battery.