It is possible that when you created the user story, it is assigned to the default area or iteration. When that happens, you will not find the ticket in you board. Even if you had it assigned to you, you will only find it in the new work items list, not in the board. To fix this, you can open up the user story and make sure you fill the iteration field with the right iteration.
Another reason this is happening is if you had assigned the ticket to yourself and the current sprint or iteration, it is possible that the current spring is not selected in the board. This means if you have selected a different iteration in your board filter, then the user story will disappear once you refresh the page. Ensure you click the filter and make sure you have selected the right/current iteration to have the user story disapply in your board.