Object(…) is not pure JSON.
Who ever produced that JSON file did not do it correctly. If you try to export a collection, from Compass for example, you will see that the object id is coded as
"_id": {
"$oid": "626c18a3d880647a888888ff"
}
rather than
"_id" : ObjectId( "626c18a3d880647a888888ff" )
You would need to modify you files to use the correct format.