I'm new but an extremely fast learner, and have gotten stuck on a song. Maybe I have the wrong idea here but this looks like a pull off to me.
Tab 20 I see as two pull off's to an empty note. But on tab 22 you have the same thing but from an open note onto an empty note?
They are "ties" not pull offs.
The half note has its duration extended an eighth.
Bar or measure 20 and 22, not tab. Incidentally it's badly written, it should be an eighth note tied to a half, not the other way around.