There is no conceivable way that nobody has noticed this
I do not think that word means what you think it means.
And, no. I was unable to duplicate the problem you're having.
Sounds like an app problem and not an iPhone problem. I suggest you look into the proper forum with your issue.
Probably the way Facebook loads long lists of friends (perhaps in general, or possibly in mobile browsers in particular).Then you're not doing what I'm describing. Open Facebook mobile in Safari (not the Facebook app). Go to a friend and open their friends list. Scroll down by swiping up in the white area between the names and pictures with your thumb. Notice the lack of responsiveness every 3-4 swipes.
Probably the way Facebook loads long lists of friends (perhaps in general, or possibly in mobile browsers in particular).
The Facebook app still works well on my iPhone