Hello,
You need to make sure that you have checked your specific product category from the categories list from the size guide.
Screenshot: https://jmp.sh/TJVFhdZ
From the product page you need to make sure that you did not check the hide category option. Also you can check from the below screenshot that I used the product in two categories but the size guide still shown.
Screenshot: https://jmp.sh/C2E3OO6
Result: https://jmp.sh/mu6fyXy
You can also check the documentation for further guidance: https://xtemos.com/docs/woodmart/faq-guides/create-size-guide-table/
Best Regards.