Fix Magento Elastic Search Indexing Issue

I'm experiencing a problem with my Magento site where Elastic Search is not indexing properly. I'm unsure when this issue started or what might have caused it, as I have not made any recent changes to my Magento setup.

The ideal freelancer for this project should:
- Have extensive experience with Magento and Elastic Search
- Be able to diagnose and fix indexing problems
- Provide a solution that prevents similar issues in the future

Please include your relevant experience in your bid.