PROBLEM: You are working in Photoshop and a menu item which you used to use has suddenly disappeared.
SOLUTION: At the bottom of the menu, click on SHOW ALL MENU ITEMS.
WHY: Adobe thinks it is easier to hide the menu items which are not popular.
ADDITIONAL SOLUTION: Go to EDIT > MENUS... and click on any item which does not have an eyeball to the right. This will allow you to select the shown/hidden menu items. You will still be able to view everything by clicking on SHOW ALL MENU ITEMS.