Lost earth is a thing in SF. Basically humanity has expanded into the galaxy so far and so long that the location and nature of Earth is ambiguous or forgotten. It's a daunting prospect for us. After all with few exceptions we live the entirety of our lives on Earth. Everyone we know or know of lives or lived on Earth. Its geography shaped our history. Its environment shaped our evolution. We are children of Earth.
It is said those who do not study the past are doomed to repeat it. How much knowledge in the form of history and literature must be lost with the location of our homeworld? Saying you are a tiny particle in the universe is one thing. The mind seldom can really grasp this, even with infographics. Saying that all we accomplished will be lost on our descendants is another thing. Not mattering to the universe is one thing. Being nothing to other humans is disturbing. Worse, it's humbling. Anyone who says they like being humbled is probably lying or only one miracle away from being canonized.
It seems the earth would be hard to lose. We would have information on the location and such in any navigations computers or at least know where to look it up. Information becomes harder to lose with the more data bases that are set up. Someone must have written it down somewhere! Why would we lose such information?
In the first place, Earth might not be there anymore. If a gamma ray burst event occurred it could destroy life in a decent fraction of the galaxy or at least the Orion Arm. It might send human worlds spiraling into barbarism. Centuries later when those worlds regained their technology and were capable of star flight it might not matter where a dead world was. Why seek out ruins and bones when there are plenty of living worlds to colonize?
A seldom seen variation is forgetting Earth on purpose. Suppose we learn of a dire threat: an expansionistic alien species killing any other species it finds. Humans might decide to colonize other worlds to ensure the race's survival. When they do so they could delete references to Earth from the colony ship navigation systems. That way human colonies can give away the location of Earth (or other colonies presumably.) Given enough time the colonists might institute a curriculum of misinformation to educate their children. Their ship fell through a wormhole. Earth was forever lost on the other side of the galaxy. They were once part of an Earth Empire of thousands of worlds but the Empire fell to civil war and much knowledge was lost.
If the evil alien menace is defeated there's every chance that Earth will come looking for its lost children.