The live preview isn’t working when editing a post.
There’s a mixed content warning in the console:
_ember_jquery-27e777857b8c0730dacfe09cb11711365d21a5db4f9ee0b85d494e4259cf6cda.js:9683 Mixed Content: The page at 'https://discourse.wicg.io/c/meta' was loaded over HTTPS, but requested an insecure script 'http://discourse.wicg.io/assets/markdown-it-bundle-44ce7be589dddfedfcc9dec272ffdde2a286729af050f016dfc7c8fd40290d06.js'. This request has been blocked; the content must be served over HTTPS.
which suggests that the problem is that
force_https needs to be enabled.