Devices from some manufacturers have an autostart function. These manufacturers are by name: Huawei, Xiaomi, LG, Asus and others. Such an autostart function prevents applications from starting automatically after restarting the device. The permission to start automatically must be explicitly set manually.
If your device has such an autostart function, tap on «Start automatically» and make changes for «Settings». Please note the application icon if you see more than one entry named «Settings». Please also note that applications set for autostart don't start immediately after restarting the device. It may take a few minutes for all applications to start.
The tutorial below shows how to deal with the autostart function of Huawei devices.