yes, you missed to set up blog page with sidebar. Category and tag pages are closely related with Blog page and until you don't have such page, category and tags pages won't display properly.
We understand but until you will not set up blog page as it has been described above (WP requires this), pages related with blog won't work as you wish.
@hofergrafik We did not changed anything in this matter so that's definitely weird. To be honest, we don't know what exactly happened. We did checked it on our end and this is not a theme bug for sure.
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yes, you missed to set up blog page with sidebar. Category and tag pages are closely related with Blog page and until you don't have such page, category and tags pages won't display properly.
Thanks!
And then I selected the just created page in "Settings > Reading > Front page displays > A static page > Posts page"
When I checked the sidebar really appeared, but also a category cloud above the list of posts.
So I deselected the page in the settings (like described above).
The sidebar is still there, the category cloud disappeared ... just like I wanted to have it.
So on the one hand I´m happy, on the other I'm wondering if this will disappear after some updates as it seems like a small bug to me.
WordPress 4.4.2 and BeTheme 11.4.