Recently updated my copy of discourse and noticed this weird little bug in the console that also prevents the preview window from loading.
[blocked] The page at https://domain.com/t/topic/4512/484 was not allowed to run insecure content from http://domain.com/assets/markdown-it-bundle-d1f9395746d57602322789f6d8cdbfcb43f414005bb7a41e18cb6fdbeede9796.js.
Only get this error when accessing the site via https. Accessing the site via regular http eliminates the problem and the preview loads as usual.
Did I miss a recent change somewhere in the setting that I need to adjust so that that particular asset gets loaded over https when connecting via https? All other assets seem to be loading correctly.