is it common for one Air Pod to just stop working

Actually yes. When i started to use one airpod on my ear, and then tried both, one stop working since it automatically detects one being used. You can change this by going to settings>bluetooth>select you airpods>automatic ear detection

No, not necessarily. However, one side or the other could fail ... or just needs to be reset.

• If your left or right AirPod isn't working - Apple Support
• If your AirPods won't connect - Apple Support
• AirPods Support - Apple Support
• AirPods Service and Repair - Apple Support