Urgent Blog SEO Recovery

Within the last week several of my highest-value blog articles have tumbled in Google, while the rest of the site holds steady. Only these few pages have been hit, so I suspect a very specific content, technical or algorithmic trigger... (Budget: ₹37500 - ₹75000 INR, Jobs: Article Writing, Content Writing, Google Analytics, Internet Marketing, Link Building, Search Engine Marketing, SEO, SEO Auditing)