So I may be able to answer your question I am not in any way affiliated with Huawei, I assume first and foremost you are on EMUI 8 when you press the square for multitasking next to the apps listed name there should be a padlock icon and that padlock should be unlocked. When you click and close the pad lock it will lock that app into being open until you unlock it again if that app requires constant data communication I do not know if the EMUI software will stop that but it will keep the open from being closed.

Recently I received the EMUI 9.0 update on my Mate 10 pro so you should be able to go into the settings then system and software update and run the new update this was also after the new year.