Please make sure the "Background Mode" option is enabled from the last tab of the app. If it still doesn't work, please try to reboot your device.
Actually that’s a well known issue on Huawei smartphones . They automatically stop some apps while they run in the background...
Please follow this guide: https://www.digitalcitizen.life/stop-huawei-from-closing-apps-when-you-lock-screen
If you still have issues, please visit this website: https://dontkillmyapp.com
Some phone manufacturers add mechanisms to kill background apps, please visit this website to learn more: https://dontkillmyapp.com
Please check that your Nanoleaf device is up to date from the Nanoleaf official app (More -> Settings -> Firmware Updates)