This happens with my A51 as well. Any app I use and happens on WiFi as well as mobile data. I have cleared all caches and I my phone restarts every night. I'm most irritated by the fact that if I'm using Google Maps for navigation and I receive a call, the phone switches to the phone call and stops the navigation. When I go back to navigation I have to start the journey again (the directions are still there...I just have to press start). It happens just like you described tho...if you switch back quickly, it's fine but leave it for 30 seconds or more and it reloads. If you're filling out a Web form and go to your Dropbox or another webpage to retrieve some info, when you go back to the browser (or if you're on another tab within the browser and return to the other tab) the page reloads and you lose what you've already done. I thought this was because of my epic mistake of buying the A51 but if you've got an S20, it must be a Samsung issue.