When importing a world, the world name (nor the file name) is appended to include “ (imported)”. So if you were to play a world called “My World”, export it to a OneDrive, then import it on another computer, it would append the name to “My World (imported)”. If you do this five times, the name would end up as “My World (imported) (imported) (imported) (imported) (imported)” Eventually, the world name gets too long for the game/OS to handle in terms of exports. See below example:
A New Era (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported) (imported)
At this point, the world name must be edited down by highlighting the entire world name. Delete/Backspace won’t modify the world name.
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After importing the world, the recommendation would be to edit the name to be whatever you want before playing or “exporting” it.

It is intentional that "(imported)" is added to a world's name, see MCPE-179037. The inability to edit the world's name is being tracked at MCPE-188261.