Migrating to HTTPS can actually improve your SEO and website rankings, as Google has indicated that HTTPS is now a ranking factor for search results. However, if the migration is not done properly, it can cause temporary fluctuations in rankings and traffic. To minimize the impact on your SEO, it's important to follow best practices for HTTPS migration, such as updating your sitemap, submitting new URLs to Google Search Console, and using 301 redirects to redirect HTTP traffic to HTTPS.