I did a migration from http:// to https:// for a big site with more than 2 million of URLs indexed on Google.
As others have mentioned I'm also experiencing a bit of fluctuation on organic traffic (-10% as measured by Google Analytics).
Things i did so far:
- 301 redirect from HTTP to HTTPS URLs
https://versions of the site on Google Webmasters Console.
- Submitted new sitemaps with the new URLs and left other sitemaps with old
I'm now considering implementing HSTS and including the site on the HSTS Chrome preload list to increase security, however since HSTS makes all traffic going to
http:// redirect to
https:// with a 307 Internal redirect, wouldn't that prevent Googlebot to see the 301 redirects?