Apps restarting after waking from screen lock

[Ralph Porter]

So I have 4 or 5 apps open and lock the phone, when I wake it up again only the app that was "in focus" when I locked it remains in the state I left it, the other apps restart when I bring them back into focus, this is very annoying since they loose the position I was at and some take a long while to initiate, I've tried removing battery optimisation from the apps in question but to no avail. Is there a solution to this?

Android 7.0 BTW