I finally found a way without tweaking the code.
In WP admin panel, Go to Appearance → Customize on the “Theme Options” section, and then go to “Post Setting”.
Choose to uncheck the “Display featured image in single post” option. This will solve the problem.
In case anyone found the same issue with the same theme (or maybe another theme), try to look into your “Theme Options” customization. Sometime the theme developer has already give the option to solve this kind of issue but we may need to browse a little further into the theme setting.
