DIAGNOSIS This is an IP address conflict or a client-specific connection glitch. The router has issued a bad lease or the device's network stack is stuck.
FIX On the affected device, forget the Wi-Fi network. Restart the device. On your phone using the Google Home app, go to Wi-Fi > Devices. Find the problematic device and tap it. Select "Pause" for 1 minute, then "Resume". Reconnect the device to your network.
IF THAT DIDN'T WORK The router's DHCP may have a corrupted entry for that device. In the Google Home app, go to Wi-Fi > Settings > Advanced networking > DHCP IP reservations. Check if the device is listed. If it is, remove the reservation. Restart the problematic device to obtain a fresh IP address.
HEADS UP If the device is an older Smart TV or IoT gadget, it may be incompatible with the default "Prioritize traffic for video calls" setting. Disable this feature under Wi-Fi > Settings > Preferred activities to test.