I answered you via email on this same problem this morning.  This is not a Qimage issue.  It is a video driver problem.  You can tell this is not a Qimage problem because the line runs through no less than 6 different controls at different locations in those controls so the problem is not with what is creating the window (Qimage) but rather what is displaying the end result window object (Windows and your video driver).

Best advice is to check the video card manufacturer's website (such as NVidia, AMD, etc.) and make sure you are running the latest driver.  Provided the video driver bug is not in the latest version of the driver, that may fix it.

Whether or not you have the line in other software is irrelevant.  Different software interacts with Windows and video drivers differently.  That's why when you look at the release notes for the latest video driver for your GPU, there's always a long laundry list of bug fixes where they fixed one in program #1, fixed a different display bug in program #2, a crash in program #3, and on and on.  Video bugs are context sensitive.

P.S.  Have you tried rebooting?  I ask because I've actually seen a Windows bug that does this in a recent Windows update.  Certain times when you use the search flyout and/or settings dialog in Windows, Windows leaves behind a ghost window that sometimes appears on top of other programs.  That's what this looks like: a ghost edge of another window (from another program) that is still appearing because the window didn't get compeltely removed when it was closed.  You can see this effect in what you posted: looks like the shadow of either the left or right edge of a leftover piece of another window on top.  This bug caused a vertical line just like the one shown and it only appeared in certain programs that used a certain color "palette".  At least in my case, the problem would clear after a reboot... until you used that Windows feature (that was causing it) again.

Here's a link for more info: https://www.thewindowsclub.com/fix-transparent-or-translucent-box-on-screen-in-windows

Regards,
Mike