https includes many details you can use and adjust, so a simple https-setup might have a good or bad quality. In the worst case a https-connection is configured without certificate.
You can test your connection i.e. here (just a random search-results for "https test quality"): ssllabs.com
One example for possible settings is the content-security-policy, but this is only one of many possible settings.
I don't know if or how far google is analyzing https-configuration before ranking and showing them in search-results but it's quite probable that pages with very bad or even blocking configuration (i.e. expired certificate) get a lower ranking.
I propose to test your page and if questions about configuration-details arise you should search or post corresponding questions that are more related to the each of the details, it's also important which server you're using as the solutions for apache-webserver and nginx-webserver usually are different, you might even use still another server.
Stepping back from https to http is usually a bad decision and I'd advise not to do it but better working on the quality of the connection.