Having the exact same issue as this locked thread, which annoyingly has no solution specified.
At some point in the past ~10 days, the preview window stopped working. The problem seems to be due to the markdown-it-bundle JS file failing to load due to a mixed content warning:
_ember_jquery-a8dcbd325e04410f036f2a791d66d8316c48c5387acdd914de99a5dd6afb3cd3.js:9248 Mixed Content: The page at 'https://discourse.bigdinosaur.org/t/testing-messagebus-updating/1345/3' was loaded over HTTPS, but requested an insecure script 'http://discourse.bigdinosaur.org/assets/markdown-it-bundle-95eab67cdea904c1edf468e5ed93ba3d0ed27da63e4428828e8a566506f74391.js'. This request has been blocked; the content must be served over HTTPS.
OP posted here indicating that they fixed the issue by specifying
proxy_set_header Host $http_host; in the reverse proxy in front of discourse; unfortunately, I already have that header set and have had it set for literally years.
I do not have
force_https set to on, because that makes Discourse break horribly (no one can log in via any method and the login window responds to everything with “UNKNOWN ERROR”). I suspect this is because that setting makes a lot of assumptions about what’s in front of discourse and it doesn’t make the right assumptions for my setup, which is:
Internet <-https-> HAProxy SSL termination <-http-> Varnish cache <-http-> nginx master reverse proxy <-http-> Discourse
It’s apparently impossible to copy the full contents of chrome’s console without doing stupid shit, so here’s a screenshot of the error.
Anyone interested in taking a look shoudl be able to trigger it themselves—just go to discourse.bigdinosaur.org, create an account, and try to post something. You don’t even have to actually create a message—just invoking the composer will trigger the error.
There don’t appear to be any entries in Logster.
Is there a setting I can change, or something? Not really sure how to proceed to fix.