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Getting a Error 404 Not Found on subcategory

I have been Googling and trying anything + plugins I can find on Google, but none of the things I tried fixed my issue.

For some reason, when I go to my
URL/category –> Works
URL/category/subcategory/post.html –> works
URL/category/subcategory –> DOESN’T WORK (https://businessanddata.org/excel/excel-general/)

For my permalink, I am currently using the custom structure as the screenshot is showing. I have check Yoast settings and don’t see anything out of ordinary. The URLs were working before the version 4.9.4.

Any help is truly appreciated!