Editor styling not working in Gutenberg 5.6.1

I run GP 2.2.2 and GPP 1.8.1 on WP 5.1.1, and have the Gutenberg plugin running, version 5.6.1.

I am running the Gutenberg plugin because I'm writing a manual and want to have the latest version on hand.

When I have the Gutenberg plugin off or an older version running, the editor is styled as it should be, with the headings in the colors and size I selected. With 5.6.1, the headings are the default for the editor, no styling.

According to the WP Slack channel, this may be because of older rules in GP:

The specificity required to style the editor has been reduced so it should, going forward, be simpler, but if an older syntax was used it could be off.

There is a Github pull request on this: https://github.com/WordPress/gutenberg/pull/14407

Is it because of this specificity issue, and GP needs to be updated, or is it something else?