The $pushAll operator no longer works in MongoDB 3.6. It should be replaced with $push + $each (refer to docs: https://docs.mongodb.com/manual/reference/operator/update/push/)

Additionally, the add_to_set method needs a corresponding version (perhaps "add_all_to_set") which adds the $each modifier. The codebase should be reviewed to make sure both $push and $addToSet are used with $each where appropriate.