In this post, I selected text
and marked it bold with two stars. But it displays for me (both in preview and after posting) like this:
Is this related to the move to CommonMark as noted in the post,
Why don't images show up in a post?.
Is there something I need to update in my browser (MacOS/Chrome) to get Markdown working as it used to?
You're using a lot of HTML in that post; that shouldn't be a problem per se but I've seen cases where this interfered with the Markdown parser (even before the migration to CommonMark).
It's best to use only HTML or only Markdown within a single paragraph in your posts. Replacing **Added 4Aug2020** by <b>Added 4Aug2020</b> should do the trick, and adding a break between <hr /> and **Added 4Aug2020**. works too.