Site traffic has plummeted. Why?

Question

Search Engine Optimization

Good afternoon.
There is a gallery site. Of all the functionality, there were only pages with lists of images (previews). The thumbnails themselves were links to the full version.
The full versions of the images are on another subdomain.
A week ago I introduced a small change - now the preview does not link to the full image, but to a regular page where there is a link to this image and all the information associated with it.
And on the same day, when I updated the site, traffic began to fall. Now, a week later, there are about 4 times fewer unique cases per day than before the innovation. I can't figure out if these events are related?
On the one hand, they somehow happened simultaneously. But on the other hand, the search engine could not have lowered me in the search results so sharply, right on the same day. He usually picked up the changes in 2-3 days.
Who understands SEO, tell me, did I mess up or the downgrade in the issue is not related to the update?

Answer 1

could, look in Yandex Metrics and Google Analytics for transitions from search engines and compare what happened before and what after.