The site has been glitching bad for the past few weeks (as of this morning 10/2/18, it seems to have resolved, but no idea how long it will stay that way). This problem existed when Yahoo owned the site in years past, also.Hopefully it's high on Oath's 'need to fix' list. After posting a question, it may disappear from the display within a few hours. If it gets moved to another category (or out and back) it will usually show up again for a while. The category movement is what usually causes you to see a question reappear (at least for a while). Sometimes questions from a few days ago will return to the display, but questions from the days prior to that may still not be visible.
You can also often find questions in the main category that aren't showing up in a subcategory. For example, if you want to answer questions in the Yahoo Answers subcategory but don't see any new ones, go to Yahoo products and look down the list, and you may find some questions that are listed as being in Yahoo Answers that you couldn't see when you were in that subcategory.