Someone seems to have removed all the tags of many recent posts from the past 24 hours or so. If the admins can address and revert the affected posts that would be great.
In the meantime, consider this post a reminder for anyone who has posted in the last 24 hours to check your recent posts. Until this is fixed, they can be quickly reverted manually by going to the "Tags" button under History in the sidebar of any post and clicking the "Revert to" button next to the correct tags.