Thank you for the response. I followed your instructions, and the taskbar app preview stopped flickering but showed on the left-hand side of the monitor instead of over the icon (which was on the right side due to the number of pinned icons (26) and text showing next to the icons, so the taskbar was filled across the monitor).

After opening the settings to combine the taskbar buttons and opening winmerge next to task manager, the flickering started again with the preview window flickering in the middle of the screen. Other times there just wasn't a preview window visible at all. 

Disabling enhanced taskbar makes the preview window behave normally again, even with taskbar buttons combined. 

Thank you,
Traci