On our website, we use different domains for several countries (.be, .ch, .fr, .com, .it). On each of them there's 3 languages (en, fr and it). So for a specific page, there's up to 15 possible versions. To prevent duplicate content, we set the canonical URL on .com for English and French and .it for Italian.
Recently, Google has decided to change the status of 613 pages from "indexed" to "non-indexed." This decision was driven by the detection of duplicate content. Indeed, Google did not select the same canonical URL that we had defined, leading to this change.
We have conducted checks to understand why Google made these choices. We looked into whether the alternative domains were more popular than the .com domain, which might explain Google's decision. However, after analysis, it turned out that articles linked to the .com domain had more impressions, clicks, and visits than those on the other domains.
Despite our careful implementation of hreflang tags to indicate alternative language versions and correctly adding canonical links following best practices, we are puzzled by the cause of this situation.