I noticed that some of my F5 http head monitors that I had existing in our 10.2 environment were not cutting over properly / they were failing in our 11.1 HF1 F5 environment. I did a little digging and found that you need to use two CLRF (carriage line return feeds) instead of one. As you can see from the screenshot below if you add an additional /r/n to the first carriage line return feed your monitor will be successful where as just one will fail. Hope this helps.