I used bulk actions to add a new category and tag to my posts and now the Markdown for all my posts are gone. While it does not impact the look of the articles on the front end, this means having to painstakingly convert the posts back to Markdown when I want to work on them in the future.
I know there are converters to do that but the output from those is different from my style of using Markdown. In particular, I prefer to use link definitions because I have several links per post that point to the same sources. So I prefer to put [link text] tags around each link and then define their source at the end of the article.
Please do something about how Markdown is saved.