Reconnection Issue

I have a Problem:
After a restart of the router the lamp does reconnect to my router but does not show up in the App anymore and cant be controled over the Server, for example for wake up mode. Thats a huge problem for me because i only bought the xiomi ceiling lamp (480) for waking me up. my router always cancels the internet connection at night and receives a new dynamic IP. Afterwards the lamp is finds the connection to the router again, but obviously not to the server.