Diagnosis
This is almost always a Wi-Fi stability issue. The camera isn't handling a weak signal or interference well over long periods, causing it to drop its connection and not successfully reconnect on its own.
How to Fix It
Start by checking your camera's signal strength. In the eufy Security app, go to your camera's settings, then "General," and look for "Wi-Fi Signal Strength." If it's fair or poor, you need to improve the connection. 1) Try moving your router closer, or use a Wi-Fi extester on the same 2.4GHz network. 2) More reliably, consider a powerline Ethernet adapter with a Wi-Fi access point, or move the camera closer to your router. A stronger signal is the permanent fix.
If That Didn't Work
The problem might be your router assigning a new IP address that confuses the camera. Log into your router and set up a "DHCP Reservation" or "Static IP" for the camera's MAC address (found in the eufy app under Device Info). This guarantees the camera always gets the same IP and can prevent these drop-offs.
Heads Up
If you have a dual-band router, ensure the 2.4GHz and 5GHz networks have different names (SSIDs). If they have the same name, the camera can sometimes get confused after a router reboot and try to connect to the 5GHz band, which it doesn't support, causing it to fail.