Update - This issue was fixed on the 2/22/2019 update.
Known Issue - As of the 2/19/2019 update District Attendance Letters (Beta) are no longer available in the navigation. Also the District Setting option to Disable School Based letters is hidden.
The pages and option will be restored in the next update.
If needed, the feature can still be accessed on the 2/19/2019 version by directly browsing to the LetterOptions.aspx page.
The other pages are available from the "Related Pages" links at the top of the Attendance Letter Options page. Once on the page, it can be added to your favorites.