The Search REST API returns 500 if called multiple times by the same account

Issue Summary

The Search REST API randomly returns 500 errors if called multiple times by the same account. 

Steps to Reproduce

1. Call the Search API multiple times. 

Expected Results

The search should work as expected, respecting the rate limiting.

Actual Results

Some requests will return below errors:

"statusCode":500,"message":"java.util.ConcurrentModificationException: null"

"statusCode":500,"message":"java.lang.ArrayIndexOutOfBoundsException

Workaround

This is an intermittent behavior. Running the search again should work.