Why do apps and tabs in Safari on iPhone 7 Plus keep reloading after being in the background?

Question

iPhone

iPhone 7 Plus 128 GB, iOS 13.4.1, bought from aStore in October 2017, never been repaired, never jailbroken.

I've been seeing some very annoying app behavior in the background for a few weeks now and it's become unbearable in recent days. About a minute after being in the background, the application restarts. For example, today I tried to listen to a voice message in VK and after turning it on I returned to Safari, but after 15-20 seconds the voice stopped, I returned to VK and saw that the application was reloading. In addition, I observed this when making calls in Zoom (I turn it off, use some other application and after 20 seconds the call ends, and after returning to the application it is loaded again). What to do? The problem existed, but on a smaller scale, even when I did not upgrade to 13.4.1, but sat on 13.4. On 13.4.1 it was updated via itunes by wire.