In the destination, unique keys are being converted to strings so updates on integer fields will not work.
Nested fields (e.g. /orders/order_item_id will create a field in mongo called orders/order_item_id) which will cause issues.
The issue in the code can be found on lines 150 and 165: https://github.com/streamsets/datacollector/blob/master/mongodb-protolib/src/main/java/com/streamsets/pipeline/stage/destination/mongodb/MongoDBTarget.java
Leading slash still needs to be removed, but other slashes need to be replaced with periods. The data type for the key should not be modified.