Create and approve loan in batch mode with transaction true fails

For pre-approved loans, requirement is to create, approve and disburse loan as part of single batch request with transaction set to true. It fails with Nil pointer exception. 
Couple of observations:
1. if enclosingTransaction=true is not specified, the request works. Only fails with transaction mode on
2. If enclosingTransaction=true is specified, and the batch request is to create loan, and approve a pre-existing loan, it works.

 sample request attached.
error msg recieved:

[
{
"statusCode": 400,
"body": "Transaction is being rolled back. First erroneous request: \n{\"requestId\":3,\"statusCode\":500,\"headers\":[

{\"name\":\"Content-type\",\"value\":\"text/html\"}

],\"body\":\"

{\\\"Exception\\\": java.lang.NullPointerException}

\"}"
}
]