Installing and upgrading help

Ok, I found the problem. The old site was http-only, and the new https-only. I hadn't updated wwwroot to an https:// url and, despite the fact that the server seems to be configured to automatically convert http requests to https, it must not have worked for some attempts. I re-did the migration for good measure, updated the url and cleared the cookies in my browser, and now everything (so far) works!