You can turn off the Character "continued" feature in Screenwriter. You do it under Format | Element Styles ... Character Name.
What is happening when the character suddenly speaks in Voice-Over? Obviously, the character was on screen until that point. Did he just vanish?
There is nothing wrong with going from plain dialogue to Voice-Over, but something has to account for the absence of the speaker who was there a moment before.
You have to distinguish between Voice Over and Off Screen.
The same character can be On Screen and speaking in Voice Over (V.O.), but obviously can't be On Screen and speaking Off Screen (O.S.).
They're two different things and mean two different things.
When someone is speaking off screen, it means that, while they are not visible to the viewer, they are nevertheless present within the physical *world* of the story -- in another room, locked in a closet, on the other end of a phone or a voice box, or a radio receiver. The point is, the voice that the audience is hearing is likewise audible within the fictional universe of the story.
A Voice Over, on the other hand -- unless you're dealing with some kind of fourth-wall-breaking, is audible only to the audience. Somebody in the world of the story doesn't hear it.
It is either a narrator speaking to *us* -- whether that narrator is someone within the story or separate from it, or else we're hearing the thoughts of a character (and we're not talking about telepathy here -- but literally hearing or being told what somebody is thinking).
But in any case, the Voice Over isn't audible in the "real world" of the story.
Only *we* -- the audience, hears it.
Take something like Goodfellas -- it's full of Voice Overs. Even different characters speak -- and *they* -- the characters in question, are always on screen when they -- the characters, are speaking in Voice Over.
NMS