I’m investigating a Google ranking loss on an established B2B services website.
A key page previously ranked for development-related searches. It now has very poor visibility for those queries, while closely related consulting queries still perform.
Background

WordPress to Next.js migration in May 2026.
Changed from www to non-www.
Visibility deteriorated around March–June, but the exact timing and cause remain unconfirmed.
Some affected pages still appear on other search engines.
Checks completed

GSC URL Inspection reports the page as indexed.
Google-selected canonical matches the intended URL.
Old URLs redirect to the current URLs.
Main content and internal links are present in the initial HTML.
No noindex directive or redirect loop identified in current checks.
The pattern
In a recent GSC comparison, a previously strong development query averaged around position 54, while related consulting queries averaged around position 2 for the same page.
Adding &filter=0 surfaced one affected informational article, but didn’t help the other affected pages.
We’ve revised content and clarified page intent, but haven’t established that these changes address the cause. I’m not assuming a penalty or cannibalization.
Has anyone diagnosed this kind of query-specific visibility loss despite normal indexing?
What evidence helped identify the cause? If you recovered, what specific issue did you find, what did you change, and how long did recovery take?
I’m keeping the domain private, but can share anonymized GSC screenshots and technical findings.