I suggested and asked about Windowblinds, since, occasionally, I see the issue on my system too, usually, when I on Windowblinds. Not sure if it just my lone system issue since I am doing a lot of software compatibility testing on this system. And usually the issue resolved if I disable Windowblinds (apply default, Windows theme). Suggested the same for Curtains, since it too skin the taskbar.
Thank you,
Basj,
Stardock Community Assistant