I hope you are well today and thank you for your question.
I can add it as displayed in the attached screenshot.
Please make sure you are using latest version of Unyson plugin and theme.
If the issue still persists for you then would you mind if i log in to your site and do some troubleshooting? If this is ok then could you please share me your site log in details privately by adding them in the box having text “Click here to share private content. Only you and forum moderators will bee able see it.”?
Yes this can be problem of your server.
This can also be due to plugin conflict on your site so please try temporary deactivating all plugins and see whether everything works fine and then enable the plugins one by one to see which plugin is conflicting if any.