Additional Product Subcategories are not showing in menu bar

[Moved from Your WordPress which is NOT a support forum.]

hello – i hope i am in the right place. i have a parent category called ‘shop by brand’. this parent category has about 15 product subcategories; however, when i go to appearance > menus to add additional product subcategories under this parent category, they will not display on the homepage menu. in fact, when i try to add additional subcategories to this parent category, the menu bar disappears on my homepage. i have also gone to screen options under product categories and increased the product category number to 100. could someone help resolve this issue or recommend a plugin. i am not a coder. Just to reiterate, i would like to know how i can get additional product subcategories to display on my homepage under my ‘shop by brand category’. my theme is called fashion.

I would prefer that these product subcategories appear on the left side when someone clicks or hovers on the parent category ‘shop by brand’. to accomplish this, do i need a plugin?

what would be a clean and simple solution?

thank you in advance