Diagnosis
The most common cause is the camera being set to 5GHz Wi-Fi, which has shorter range and is less stable through walls than 2.4GHz.
How to Fix It
Make sure the camera is on your 2.4GHz network. You'll need to factory reset it (hold setup button 20 sec), then during re-setup, ensure your phone is connected to your 2.4GHz band, not 5GHz, before starting.
If That Didn't Work
Power issue. The Gen 2 can be sensitive to underpowered USB adapters. Swap the power adapter for one rated at least 2A (like the one that came with an iPad). Avoid using USB ports on computers or cheap power strips.
Heads Up
Check for Wi-Fi congestion. If you have many smart devices, your router might be kicking this one off. A simple router reboot can sometimes resolve this.