This issue occurs due to the HTTP and HTTPS mixed content issue. There are many ways to combat this change, but the easiest way to do it by using the SSL Insecure Content Fixer plugin. It is a free yet powerful plugin you can use to resolve a variety of WordPress mixed content warnings and errors. After you install it, it automatically works to detect insecure content on your website.

It also provides multiple levels for fixing mixed content errors, ranging from Simple to Capture:

Once you select your detection level and settings, this free plugin will take care of the rest.