E-commerce Site Indexing Issue Fix

I have a sizable E-commerce website with 90K pages. Initially, 40K pages were successfully indexed in Google Search Console. However, a troubling trend has emerged: all pages have been deindexed, and now, only the home page remains indexed. I require an expert to identify and resolve the indexing issues.

Key Responsibilities:
- Diagnose the cause of deindexing
- Implement necessary changes to restore indexing
- Provide insights for future prevention

Ideal Skills:
- Extensive knowledge of Google Search Console
- E-commerce site optimization experience
- Proficient in identifying technical SEO issues
- Familiarity with large-scale website management