Problems relating to the depth of menus

Hello,
First of all, I want you to understand in my poor English.

I made a structure of 4 levels of depth on one of my website’s menus.
However, there is an error in the page from levels 2 and 3.(the first and last levels works well.)

For example, below page, which is the first level in the fourth depth, can be viewed well.(though unfinished)
http://ingrao.cafe24.com/product/
Similarly, below page works well on the last level.
http://ingrao.cafe24.com/product/equipment/storages/refrigerator/

However, the second level and the third level, doesn’t work message with “page not found”(In the browser’s tab name, you will find this message in many of the Korean languages.).
http://ingrao.cafe24.com/product/equipment – second level
http://ingrao.cafe24.com/product/equipment/storages – third level

Although the contents of the page are not completed, it is abnormal to display the message.
So, I want to solve this abnormal problem and want the contents of the page to appear normally in the pages.

I don’t know whether my intentions are well understood due to poor English skills.
Anyway, can you help me solve this problem?

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In addition, I am using Enfold Theme with several plugins such as uber menu.
However, after disabling all plugins, it seems that the problem is not the issue of plugins.