Custom HTML "An unknown error occurred" mixed content error

[Forecaster]

Describe the bug
When trying to use the custom HTML block the following is shown:

It appears to be unable to load the code editor because it's trying to load it via http on my https site. So the script is blocked.

To Reproduce
Steps to reproduce the behavior:

1. Have SSL enabled site
2. Try to use Custom HTML block
3. Observe Mixed Content error hopefully?

Additional context
Using Gutenberg 3.3.0
Just updated in fact and unfortunately the issue remains.

Running WordPress 4.9.7 on an ancient Ubuntu Server 12.04.5 box, with a very old PHP version (unfortunately)

[designsimply]

Tested and confirmed and noting that I saw a different warning in the console:

Loading failed for the <script> with source “https://cute.wordpress.com/wp-admin/undefined/wp-admin/load-scripts.php?load=wp-codemirror,code-editor,htmlhint,csslint,jshint,htmlhint-kses”.

^{Tested with WordPress.com and Gutenberg 3.2.0 using Firefox 61.0.1 on macOS 10.13.6. Note: I used 3.2 for a quick test but it would be nice to have an additional confirmation with a later version. 😊}

[tofumatt]

It seems like there is an unrelated bug in latest master with http sites; I get TypeError: potentialIframe is undefined trying to replicate this on an HTTP site. 😢

[tofumatt]

#8211 will help in debugging this but I don't think I'll get to this today so moving the milestone. Sorry 😞

[Forecaster]

It's fine. There's a workaround in Chrome. It has the option to allow insecure scripts to load which allows the HTML editor to work until the next session.

[arekkopczynski]

I have had the same error, during developing webiste on address http://site.com HTML block work's fine. After change domain and activate https - HTML block display error. For me helped set addres in wp-config:

define('WP_HOME','https://site.com');
define('WP_SITEURL','https://site.com');

[Forecaster]

This solution worked for me as well. I didn't know about these statics before.

[designsimply]

I re-tested today on an SSL-enabled site, with the proper HTTPS values used for WP_HOME and WP_SITEURL, and the Custom HTML block did not display any errors when I tested it.

Closing as resolved.