Hello Basj -
I disabled Start 11 Enhance Taskbar and the flashing icon went away. When I re-enable, the flashing icon is no longer there, however when I reboot (with Start 11 Enhance Taskbar still enabled), the flashing icon is back. Also, after disabling Start 11 and reenabling with it not flashing, if I restart explorer the flashing icon returns. It appears to move laterally 1/2 icon position on the bar depending on whether or not I have minimized applications on the taskbar also. Here is a link to a video showing the flashing icon: Video Link
Thanks!