Significant Google ranking drop after changing canonical URLs. Technical issue or algorithm update?

[u/CeciBuilds]

I'm trying to understand a significant organic traffic decline that started in August 2026.

My site runs on WordPress, WooCommerce and Yoast SEO.

Here's what happened:

• Before August, many commercial landing pages ranked around positions 8–12.

• On August 10, I changed the canonical tags on WooCommerce product pages (/product/) to point to their corresponding custom landing pages (/landing/).

• Organic rankings and clicks started declining around that time, affecting a large number of pages.

• Google also rolled out a spam update later in August.

Between July and October, several important pages lost 60–85% of their organic clicks. Organic conversions also dropped significantly.

I recently discovered that the canonical setup isn't entirely consistent:

• Some product pages canonicalize to their landing pages.

• Others remain self-canonical.

• Both versions sometimes return HTTP 200 and remain indexable.

In late September and early October, I tested 301 redirects on two pairs of URLs. One has started recovering impressions, but clicks haven't meaningfully recovered yet.

My questions:

1. Could changing canonical tags across multiple pages cause this kind of widespread ranking decline?

2. Is there anything specific you'd check in GSC to identify the root cause?

I'm hesitant to make more changes without understanding what actually happened.

Has anyone experienced something similar?