Launcher does not take its own app. All open apps can not be killed. Last app left after killing all the apps is always left open.
After opening a set of apps at the time of killing apps the last app can not be killed. Seems like the launcher clings to last used app and it is treated as launcher app which obviously can't be killed by any means. It may be the case issue is Le Eco 1s specific but I did not experience it in any other launcher.