When using Power Saver mode with your mobile device, it tends to restrict background services and whether they run all the time (such as location, automatic updates and VPN services). Because of this, VPN services can be disrupted when running in power saver mode and potentially leave you vulnerable. In some cases, there are power saving modes that are extremely aggressive resulting in the VPN not being able to connect at all.
If you are experiencing issues with the VPN staying connected or it is simply not able to connect in the first place, please turn the battery saver feature off. Keeping your device charged up will help keep yourself safe and prevent these issues.