The question list on single category page is not correct

Hey, when I check the single category page, the question list confused me,
I created 3 categories, Notification/Activity/Skill, and posted 1 question for every category. then I got the list like below:

The category Notification (there is only 1 question in it, but 2 question items displayed on there):

The category Skill (there is only 1 question in it, but all 3 question items displayed on there):

I had try to switch the theme to wordpress default theme, and same issue I got.

Anybody can give me some suggestion?
Thanks.