Hi @milouze,
Your case is unusual, and we appreciate your efforts in doing some testing and research on your own.
However, I followed the same steps to test with the WordPress category, and it works in the same way: siteurl.com/category/blog/category/blog/
The issue may be related to how WordPress handles URLs, and your idea to ask the question in the core track could also be helpful.
In the meantime, I also recommend creating a bug report in our GitHub repository. This will allow our development team to look into the issue directly and potentially find a solution.
Please include all the details you’ve shared here and any other relevant information that could our developer understand and replicate the issue.
Thank you for your patience and cooperation.