JSON is not properly turning an object into a string

I am making a game and am working on the accounts. When i have JSON stringify the object and save it to a file, it sometimes (occasionally and at random) writes:

{"[email protected]":{"email":"[email protected]","password":"myPassword","token":"c26a2a66-77f8-43d7-aa92-14da81979386"} >}< "[email protected]":{"email":"[email protected]","password":"myPassword","token":"209758d0-9a6e-4e99-835a-21595b822796"}}

when i am expecting:

{"[email protected]":{"email":"[email protected]","password":"myPassword","token":"c26a2a66-77f8-43d7-aa92-14da81979386"} >,< "[email protected]":{"email":"[email protected]","password":"myPassword","token":"209758d0-9a6e-4e99-835a-21595b822796"}}

My Code:

fs.writeFile('save_info/users.json', JSON.stringify(User.USERS), err => {});

What is going on?