Selected VM category does not appear on the page

[yan77]

Hi All,
I am experiencing a weird problem and could not really figure out why this is happening.. Any help would be really appreciated. I have basically below structure in VM;

Top Category A
   - Sub Category A
      - Product 1
      - Product 2
Top Category B
   - Sub Category B
      - Product 3

and I have 2 menu items,

Menu Item 1;
   Menu Item Type; VM Category Layout
   Select a Category; Sub Category A
In this menu, everything works correct, both Product 1 and Product 2 are displayed under the menu item correctly.

Menu Item 2;
   Menu Item Type; VM Category Layout
   Select a Category; Sub Category B
In this menu, the Product 3 does not appear at all (it appeared once, but it got disappeared once I refresh the page) but Product 1 and Product 2 are displayed instead even though they should not be! The Sub Category A is even not selected under this Menu Item 2, I do not know why Product 1&2 get to be listed on the page but the Product 3 does not appear at all!

I appreciate if anyone can give me a hint, I have no idea how to address this issue.

I am using VirtueMart 3.6.10 , and Joomla 3.9.16 and a third party Joomla template.

Thank you!
Yan