I have a patio door which has a handle about half way up. The tip of
the handle points straight up when the door is shut & locked. Turning
it 90 degrees so it is horizontal allows the door to be tilted from the
bottom (opening at the top) to allow air in. Turning the handle 180
degrees, so the handle tip points straight down and pulling it towards
me allows the door to be slid open.

Trouble is, its a bit of a bugger trying to get it shut properly so I
can lock it. Often the handle will get stuck in the horizontal position
and therefore won't shut & lock properly. Sometimes I can get the door
shut in one movement without any problems. Othertimes it can take 6 or
7 goes. Whatever knack there is to this - I dont have it!

Is this a sign that the handle is wearing out perhaps?

Is it possible for a company to change the door from a tilt & slide
mechanism to one that just slides open/closed? (I think I'd find that
easier)