It seems your account is one of the first to have the updated sorting & filtering features which has also changed the way that fields can be displayed in projects. It seems that the Customize menu will only show your custom fields and not the 9 metadata fields anymore (assignee, due date, tags etc) which have been relocated…
Look for the new ‘Show fields’ button on the left side, near the Add task button, your Tags should be available in the dropdown menu