When I highlight a word or phase for deletion, quite often the cursor deletes the words in the line above instead. I reduced my cursor size to the minimum: Normal in Apple Preferences, but it made no difference. I couldn’t find how to change the size in Scrivener 3, to see if that stopped the problem. Note that I’m using Catalina 10.15.4 and a font size of 24 when writing. Anyone else come across this problem?
Do you see similar issues in TextEdit? If you’re selecting text with your mouse or touchpad, do you see misalignment in other applications?
In Scrivener, low level operations like selecting and deleting text are handled by the Mac OS text toolkit. This kind of behavior probably points to a system-level issue.