problems when using blog functio and one category instead all categories is seen

Hi!
I use Joomla 5.0 and having some troubles with pb 3.1.0.
When I create a new article and using the blog function then I having trouble showing just one category.
I have used the articles source and choosen just one category and when I go to the frontend, to see the result, then several of articles of all categories start to appear in a stream. It slows down my web site.
I don't know why, because I've used the same settings as my other articles but with my new category (it's a story about my move to a new apartment). My other blog pages is working as a charm so I don't know what to do. is it a bug or is it me?

Hi
Please check the tags option, do you have it enabled or disabled ? just under the category option
CEd