Using viewport width
If you use 100vw (viewport width) to limit content width on a page that is vertically scrollable, this can be a reason for a small horizontal scroll.
Example
If you don't see any horizontal scroll, you are not safe yet. The appearance of horizontal scroll can be dependant on your scrollbar settings, browser, OS and connected devices (mouse), so always test the website before release. If you see the horizontal scrollbar, it's due to width of the section being set to 100vw.