I am involved with three separate websites using 126.96.36.199, 188.8.131.52, and 184.108.40.206 respectively. Each is recently upgraded and none now display the custom sidebar items previously created. The Custom sidebar plugin appears to be activated and the data is still there. New sidebar items created now do not show either. I have read other threads but none are within my remit as we need our host for any server / PHP reports.
What version did you upgrade from? If from version 2.x, and you had elements in the right sidebar, these items would be orphaned in 3.x.
Does this seem to describe your situation?
No, we upgraded from 3.1. I am just wondering if we missed the fact that the sidebars went missing a long time before but that is unlikely. Also attempts to create a new item can be saved but then they do not appear.
(Re-posted here: Custom sidebar not working at all)