Mobs despawn after leaving the game itself even if it is a tamed or a one spawned from a spawner egg

Whenever I call it a day (meaning leaving the Minecraft game inactive) mobs generally despawn even though after I already tamed or spawned one from a spawn egg. They generally despawn every time I go back to my server! Can you fix it. I’m pretty sure that the spawning mechanic is broken after I updated my Minecraft app to 1.17.30. When I already got back online in Minecraft. my server is eventually different from before. No mobs are left. Not even a single tamed mob. It is what it is. Can you fix it? The spawning mechanism is broken