I, actually, made some widgets “always hide”. I thought they wouldn’t appear in the panel. Instead I got the expand or plus icon.
Though this issue is resolved, how do I remove some widgets from the Status Notifier? Because, there I can only find options for showing or hiding them, but not permanently removing them.
Usually this is done by reconfiguring and/or not running the programs that produce the widgets. What are the specific Status Notifier widgets you would like to remove?