Ring Doorbell doesn't connect anymore

I have been using a Ring Doorbell since December 2017. On 20-4-2020 the connection to my WiFi network was suddenly lost. I can connect an identical Ring Doorbell from a friend to my WiFi network. I have given my Doorbell a hard reset and tried connecting it to the network in my friend's house. It is also not possible to connect the Doorbell to this network. I can go through the connection procedure completely according to plan. But the last step: Doorbell will now not connect to the network. It ends with blinking white in the right half of the ring. Also in the advanced option, I entered all network parameters manually, but without result. Battery is full charged. How do I find out why the Doorbell can no longer connect. Please your help