We did a install aster testing the Invision Community v4.6.11 Beta 1 and the default theme is displaying incorrectly. All the items that should be the sidebar are at the bottom of the forum.  stacked on top of each other.  If I turn them off the forum looks ok but when I refresh the screen (even after clearing system cache and local cache it comes right back)  There is only the default them installed at the moment and I downloaded a clean copy of the default them from test site.  Logon details for the site are current in client profile.

Have you tested turning off all applications/plugins (in addition to using a clean/default theme which you said you are using)

1 plug in was causing the issues

I’m glad you were able to get to the bottom of the problem!