[PAID] Need someone to fix bugs and errors on my Discourse forum

I found the problem. It was in the site’s CSS:

#ember19 {
  display: none;

If you have code like this Discourse warns in the CSS editor:

Sorry – using #ember or .ember-view CSS selectors is not permitted, because these names are dynamically generated at runtime and will change over time, eventually resulting in broken CSS. Try a different selector.

Presumably this was used to turn off some element of Discourse in the past, but the id was assigned to a new element after the upgrade. Whatever the case, removing this code fixed the problem.