dumpとれたみたいだからrestoreしようとしたんだが
It's probably too late, but I was facing exactly the same issue (mongo 2.4 to mongo 3.6 dump) and the solution was to create the database and the collection manually, before doing mongorestore. This probably jumps the create part of the statement and so avoids what I think is an import bug between different versions of mongodump/restore.
https://stackoverflow.com/questions/47767955/what-is-create-in-mongo-dump-files
仕方ないから全部のコレクション作ってからrestoreするなど。
どうにか入ったくさい...んだが、indexの構築が...はぁ。
