Windows 11 Enterprise, 24H2, build 26100.4349, Windows Feature Experience Pack 1000.26100.107.0
The blank vertical taskbar issue is still present in the 2.53 release. I haven't determined the threshold as to how long after boot up you have to wait to login before the problem manifests itself. When it does, all vertical taskbars on all monitors are completely blank--except the clock appears on my secondary displays but not my primary display. Clicking where the start menu button should be, on all monitors, activates the start menu correctly. The first time I restarted Explorer from Start11, the icons on my 2nd monitor did not shift to the right, so the vertical taskbar partially hid the first column of icons. Restarting Explorer again fixed it.
Windows 11 Enterprise, 24H2, build 26100.4349, Windows Feature Experience Pack 1000.26100.107.0
(Despite these glitches, I can positively say that this new experimental vertical taskbar feature is the sole reason I bit the bullet and upgraded to Windows 11 ahead of the October deadline!)