Running v 1.14 of plugin.
I was troubleshooting another problem and had to switch themes several time and also deactivate the plugin. When I reactivated the plugin with the same original theme as before the troubleshooting, the OTW sidebars don't show on the widget pages.
I did not upgrade the plugin. But I still tried one of your suggested solutions. In widgets.php, a search finds no text with "otwrem".
This makes me nervous because I might have to deactivate plugin again someday. I'm just starting with it so can abandon now easily. I don't want to build a bunch of pages that break for me or my client later.
Why did this happen? If I can easily get my sidebars to show on Widgets page, I will. But I'm very nervous about it happening again.