AWS Open Search Giving 429's - Metrics Don't Add Up

Open Search Service - 2.3
ElasticSearch - 6.4

We have been dealing with an ongoing issue of our calls to AWS OS Service giving 429 - Too Many Requests. This will happen intermittently throughout the day where our indexing and searches will receive this error. However, when we look through our metrics, we aren’t seeing any correlation with our metrics. Indexing and search rate are reasonable. We rarely see things enter the queue and have 0 queue rejections. Our CPU is stable and not maxed out.

After looking through the docs, these are what the AWS docs suggest as the culprits for 429s. I guess I’m asking for ideas of where else to look. Is there a different metric we could correlate these 429s to? Is there some other configuration in AWS that might be causing this?