Doorbell 2 suddenly disconnected, won’t reconnect

Doorbell 2 and chime installed a week ago. Hardwired and good wi-fi connection. Set up smooth, no problem. Suddenly, overnight, feed to video stopped and no tone notification. Repeated attempt to re-connecting device through app failed. App shows good power supply and wi-fi, bell & chime 'on-line'. However, elsewhere on app, physical installation, chime connection & motion settings have green tick but says (in red) 'required'. Have tried several times to repeat set-up process pressing orange button on bell. Sometimes it says connected to wi-fi, other times, wi-fi connection failed. But, good wi-fi signal from router throughout and other devices (phone) have signal. I do not understand why this should suddenly stop working and/or fail to re-connect. Or, how to resolve it! I do not know if this is a hardware or software/app issue. Any help gratefully appreciated.