How do I prevent a specific app from ever running in the background

So I have googled a lot and mostly I end up with apps such as Greenify and other obsolete "close all apps with this button". But that is not what I want. My specific problem is as follows:

I play Pokémon Go all the time - I love it. But very often, if I go to an other app, close the app, turn off the screen, whatever, Pokémon Go gets stored in RAM. This is awesome in so many circumstances, I totally get it, but Pokémon Go specifically somehow loses it's connection to the servers and waiting never fixes it. There is one simple solution, closing the app manually and opening it again. I have even experienced this after just switching app to select the next song to listen to and voila, Pokémon Go doesn't work. It's extremely frustrating, because the app doesn't tell you anything, you have to figure out yourself by noticing no Pokémon are showing up. I imagine I've lost hours of potential Pokémon/kilometers already.

So, is there any way I can choose Pokémon Go to never get stored in RAM and still keep that functionality for other apps? I will root if necessary.

Thank you