From what I understand, the “offline” issue is mostly caused by unstable Wi-Fi communication between your HB3 and your Eufy device. In most cases, it can recover on its own within 48–72 hours.
The HB3 has two operating modes, and Performance Mode usually works best.
A 7-meter distance is generally not considered out of range, but walls can weaken the signal depending on the material.
If all of your Eufy devices are using 2.4 GHz Wi-Fi, the best way to improve stability is to reposition the HB3 or the camera—ideally by adjusting placement vertically (not just horizontally) to get a stronger signal.
One additional workaround I recently found: if you have a Eufy S350 indoor camera (which supports 5 GHz Wi-Fi), you can use the Multi-Bridge feature to reduce reliance on the HB3 and maintain a more stable connection. However, you’ll need to separate your router’s 2.4 GHz and 5 GHz networks into two different SSIDs. A combined/mixed SSID usually won’t work well.