I am having the same problem with my sons Huawei P 9 lite. I just received the following response from Eset- support (BTW: Thanks to support for the very fast response!!):
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Huawei for some models integrated system task battery manager which kills every app which is not used for some time.
We are working from background…
Solution is to manual change this settings in child device:
Settings/Advance Settings/Battery manager/ Protected apps
Please let us know if this helped .
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I will try this later and post my experience.