Signal strength

Hello, this is my first visit. Installed Ring doorbell 2 weeks ago but it's a bit hit & miss what it picks up. Examples : Sometimes it picks up motion & rings the chime unit but not the app on my phone, sometimes it's fine : If I'm out, it is slow to notify me there's someone at the door, by the time I've realised, the caller has gone: Quite often the message " activating device" is present for a long time. I thought it could be my WiFi speed but I've had that checked and it's fine, both indoors and outside where the doorbell is. In the device health check it tells me that the RSSI -66. I don't know what that means. What can I do?