Every time you minimize Minecraft it reloads.

When you are in a world and this happens you do not get disconnected, however if there are any other players in the world they seem to get disconnected most of the time.

If you're in a server you will get disconnected though.

This happens since 1.16.20

Steps to reproduce:

1. Join one of your own worlds with someone else   OR   join a server
2. Minimize the Minecraft window
3. Open the Minecraft window

Outcome:

If you joined a world:

Minecraft reloads, but you are still in the world. The person in your world has been disconnected.

If you joined a server:

You have been disconnected.

Expected behavior:

Minecraft doesn't have to reload and the other player doesn't get disconnected

AND

You don't get disconnected from the server