Just realised I replied to the wrong person, oops sorry! 
You shouldn’t need to change your @transition command to ‘in 0.5’ (for example) it should work fine with just the number after transition. For example, I use @transition fade out white 3 (A LOT!)
Sometime’s these things can be super finicky!
I would also have suggested:
@transition curtain out_left
(BACKGROUND NAME HERE)
&CHARACTER stands screen center AND CHARACTER faces right
@transition curtain in_right
However, if that’s not working, perhaps try adding INT. BLACK - NIGHT in between to pause it black for a moment perhaps?
e.g.
@transition curtain out_left
INT. BLACK - NIGHT
@pause for 0.1
INT. BACKGROUND NAME HERE
&CHARACTER stands screen center etc…
@transition curtain in_right
It’s not guaranteed to work, or be super smooth but it might transition it somewhat smoother.