Google Explains A Weird Domain Migration Outcome

Migrating To Different Domain NamesThe person asking the question maintained three websites under three different country code top level domains (ccTLDs). The project was a migration from one domain name to another domain name, each within their respective ccTLD, like example-1.fr to example-2.fr. Thus, because everything about the migration was equal the reasonable expectation was that the outcome of the migration would be the same for each site. Two out of the three site migrations failed and lost traffic. The important takeaway is what Mueller said, that they’re all different sites and so the outcome should naturally be different.