This is happening because there are no widgets added.
Please add at least one widget to the blog sidebar.
The blog layout of this theme is supposed to always have a sidebar, like here.
You can find info on how to add widgets to the blog in the following sections of the User Guide:
“7. Blog widgets setup”.
In case you’re not sure where to find the User Guide:
Please go to themeforest.net/downloads. Find the theme and click ‘Download’ > ‘All files & documentation’. Download and unpack the zip file. The User Guide will be in the ‘Documentation’ folder.