This is only happening when clicking the minimize button (in Windows 10) - the window instead gets smaller with a line down the middle. I can still minimize to the systray from the File menu, or after clicking the close button and selecting "Sys Tray". Upgrading to the latest version had no effect.

Thanks Mike.  Turns out under edit, preferences, when Qimage Ultimate is Minimized, the option somehow got changed to "Normal" instead of "System Tray".  No idea how that happened unless perhaps there is a keyboard shortcut or something else I did inadvertently. 

With the "Normal" option it does minimize to the task bar, but when I click Qimage on the task bar it opens to the smaller window with a line down the middle and has to be manually returned to full screen (the way it was before clicking the minimize button).  My Nvidia driver (studio version) is up-to-date, but I did recently replace a second monitor with one that has a different resolution and is also set to scale text differently (it's not the monitor I use for Qimage, just an extension of the Windows desktop) - perhaps that has something to do with Qimage not automatically restoring to full screen?