Don't worry, this is a completely normal phenomenon! After the firmware upgrade(only for EU countries), the device will disconnect temporarily. You just need to follow the quick steps and try to re-pair the camera and the monitor.
Click and find the Power on and Connection Instructions:
First Use of Baby Monitor BM03 -1080P High Performance Video
First Use of Baby Monitor BM04 - 5 Inch Dual mode Smart
After waiting a few seconds, the connection will be restored normally. If you still have issues, you can escalate to the manual support.