Diagnosis
This is a network bandwidth issue, either on your home upload speed or the camera's connection to your Wi-Fi router.
How to Fix It
First, test your internet upload speed. You need a minimum of 2 Mbps upload per camera for stable HD streaming. If your speed is low, contact your ISP. Then, move the camera closer to your Wi-Fi router or add a Wi-Fi extender on the 2.4GHz band.
If That Didn't Work
Reduce the video quality in the camera's settings. Go to Device Settings > Video Settings and set Video Quality to Standard instead of Best Quality. This lowers bandwidth consumption.
Heads Up
The camera streams to the Arlo cloud first, then to your phone. Slow loading is often due to slow cloud processing, not just your home network. Peak usage times can cause this.