Just removing page argument from shortcode did it. As I said many times to remove page argument from shortcode.
Passing a page argument force shortcode to render a specific page.
First make sure categories page exists and it is selected in AnsPress page setting. If you still get 404 make sure to save WordPress permalinks to flush rewrite cache.
Try to save the permalinks again, first the wordpress permalinks (twice).
(Settings -> Permalinks)
After that, go to the anspress option page and save the permalinks there.
(Anspress -> options -> general tab -> permalinks section).
I’m developing a site with this plugin and the askbug theme, and sometimes while I’m moving between versions I get a 404 error, but after I save the permalinks again the problem is solved.