This issue was also a problem in 1.2.1 and has not been fixed in 1.2.5.
Trying to make a text selection to edit in Scrivenings with typewriter mode on, it appears as if the typewriter mode is trying to keep the cursor centred as it selects, resulting in jumpy and difficult selection. The page scrolls up instead of the selection progressing down the page. This is not how it behaves on a normal single Scrivener document, where even with typewriter mode on it is possible to select down the page without it moving when selecting text. It would make an enormous difference to the ease of editing in Scrivenings with typewriter mode if this was fixed.
This was driving me crazy also. However, if you go to this thread
[url]https://forum.literatureandlatte.com/t/disabling-enabling-typewriter-mode-in-full-screen/16130/1]
it may solve your problem. Shorter version: I just discovered Ctrl-Meta-T enables/disables typewriter mode in the full-screen editor.
The “Meta” key is the Windows key.
While its nice to know its possible to work around the problem, I really like typewriter scrolling. I think the jump behaviour around the cursor in that mode is a bug which should be registered and fixed!
Oh yes, it’s a bug and on our list; sorry I didn’t confirm that here.
Thought you might like to know that this issue has been fixed in the new beta version. 
Its NOT fixed in my Windows Version 1.5.3.0 (or it came back?). The Cursor in Typewritermode is still jumping around which is really annoying. Using Cmd+Ctrl+T is just a workaround. 