Hi,
In 4.7.19 we changed the default for 'Cloud Spam Content Analysis' to on, it'll only apply to users that have less than 5 posts or haven't posted in 6 months. You can disable this if you wish in AdminCP > Smart Community > Spam Analysis, but I think you may want to change your permissions instead (see below).
However, it does look like you have guest posting enabled which isn't the 'post before registering' feature, if you prefer to use that feature to have your guests register, you would need to edit the group permissions for 'guests' and remove their ability to post or reply. I know that seems counter-productive but that will allow that feature to work.