Forgive me if this is a duplicate; I don't see the same issue.
I added some ABCjs examples to an answer (https://music.stackexchange.com/a/115586/78419) and, as expected, saw the familiar "C e a etc" snippet that displays when your actual code fails to render. I refreshed and saw my example.
However, even quite a while later, if I return to the page (via the dropdown from the "inbox" icon in the top SE nav bar), I still see the default notation snippet and have to refresh to see my example. I'm concerned: would the OP or other newcomers to the page see the correctly rendered notation? Or am I just having trouble because it's my post?
I tried pasting the URL into a private browsing window and it rendered with no problem. That suggests that the only reason I ever see problems is because I've previously visited the page. But the question stands; would any other visitor have trouble on their second visit to the page?