To summarize, to avoid misunderstanding: Your project(s) open with the horizontal scrollbar (of the source editor) being scrolled. (Hence you are missing several chars at the left of each line)?
There isn't such a setting, i.e., nothing that matches your description.
There is definitely no setting for a "default scroll".
There are several things that may be related (but I can't tell if they causing this for you).
1)
The position of the horizontal scrollbar is saved in the project session. (same as vertical scroll, and caret/cursor pos / selection...).
This position is restored when a file is opened again. That can be when the file is opened while the IDE starts up, or when you open the project.
But this can also be, if you open a specific file (e.g. via file > open) and that file had been open before (as part of the current project).
Modify the project after you did reset scrolling, make sure the project (and with it its session) get saved, and see if it keeps happening for that project.
2)
The caret pos (and selection) is restored.
If the width of the source editor has changed, then that could force scrolling. Actually, I am not sure... The saved ones should have precedence.
But maybe if some extra installed package changes the size of the source edit... Yet, I wouldn't know any that does.
Anyway, for that to be possible the cursor would have close to the right border of the editor (before you press Home or move it by any means).
If you have more than one source tab: Does it happen to all of them? Or just to the one that is active/visible when the project is opened?