The blocks occur on all post types be it a status update, a photo upload or link posts where the content is exactly the same or mostly the same.


Some facebook users knowingly or unknowingly abuse it's communication tools. Annoying others with too many messages or friend requests (though you may not know that you are actually doing that) or deliberately spamming others for commercial gain. These are completely unacceptable on facebook.


These are a few examples of how facebook detects spam.


Here: http://www.johnkingsblog.com/2017/06/list-of-message-phrases-facebook-blocks.html