Hi @info2grow,
Thank you for your questions.
While editing a post in the sidebar section I get a list of all my theme sidebars as dropdown menus. I am using the WPLMS theme which has a sidebar manager. Could this be a conflict?
I am not sure what you meant by “editing a post in the sidebar section” but i think you are talking about the Sidebars section displayed in the post/page edit screen as shown in your shared screenshot.
This Sidebars section is displayed by Custom Sidebars plugin so that you can display different custom sidebars in place of default sidebars for different posts/pages.
Also when I pick one and save it does not save the selection and no sidebar shows in the post.
I have tested it on my test site using latest version of Custom Sidebars plugin & default WordPress Twenty Twelve theme, it worked fine for me.
This can be due to plugin/theme conflict on your site.
You can just try on your development site using default WordPress theme like Twenty Fifteen and deactivating all other plugins as displayed in the following flowchart to know which theme/plugin is conflicting if any.
https://premium.wpmudev.org/wp-content/uploads/2013/12/Support-Process-Support-Process.png
Kind Regards,
Vinod Dalvi