25 May, 2021 UPDATE:
According to Microsoft, the problems caused by installing KB5001337 (see below) have been resolved in the Windows update KB5003169 (click here for more information from Microsoft). If missing scrollbars in AGi32 is an issue, please update Windows with all available updates, including "optional" ones but excluding any update with "preview" in its label.
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This is a behavior that started in late April 2021, doesn't seem to affect all users, and is related to one or more Windows Updates. This is NOT an issue directly related to the AGi32 installation and AGi32 is by no means the only program affected negatively by this update. There are even reports that some of Microsoft's own programs stop working correctly with the update installed.
Users who have experienced the problem have found that uninstalling the Microsoft Windows Update KB5001337 has solved issues with scroll bars in AGi32.
For more on this issue, please take a look at Microsoft's Support Page on KB5001337 and scroll down to the "Known issues in this update" section. Issues with this update affect all sorts of programs, including some Microsoft programs, and are not limited to AGi32. Until Microsoft releases a Windows update the corrects all the problems caused by this update, the only solution is to uninstall the update.