Welcome to Android Central! Normal Android behavior is for apps to remain paused or cached in RAM after you exit from them, in order to switch more efficiently between apps. When RAM is needed for a new app to be opened, the system will determine which app currently residing in RAM should be closed. Nowadays, more and more manufacturers implement more aggressive RAM management that closes apps more readily from RAM (even if no new apps need the RAM) in an effort to save battery. However, this also causes apps to open more sluggishly, since they have to completely reload into RAM (which also takes extra energy).
If you find that the S7 is killing apps from RAM for no need, then go to the Battery Optimization setting and turn off optimization for apps you want to protect from being killed. And if you have a 3rd party "RAM booster" app, get rid of it.
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