When we copy a .accdb file or overwrite a .accdb file a backup file is immediately created
My emphasis added.
Would that be the front end file, the back end file, or is this a monolithic (single-file) database?
Are you doing this from inside the DB itself or is this a manually performed or automatically performed copy operation using something other than Access itself to do the copy?
When you do this operation, does the thing you use to make the copy give you any messages?
The behavior of automated backups strongly suggests, as Adam has mentioned, that something is corrupted but we need more information to decide whether this is Access itself doing something or whether something else is doing this for you.