How to keep GPS fixed?

This post is not about problems with getting a GPS fix, if that’s what you are looking for go here, here or here.

My question is: Once you get a GPS fix, how do you keep it?
For me the only App that keeps my GPS fixed is Mozilla Stumbler. Whenever I don’t use it - even when I use OSMand to navigate - the GPS fix is lost every time the screen turns off or I switch Apps (exit wichever App is using GPS).
I’m not using Google Services.

You can activate the Osmand background service by clicking the satellite in the map view: