For the last 5 years I have been saving my form (while working on it) by clicking on the Field Rules button. Not sure how I picked up that habit but just found that it works and it is close by. Now in 10.4.2.381 that button no longer saves the form, I can tell because any fields I add are not listed in the field rules area after clicking the button.
Now I save the form by pressing F5 on the keyboard. Is that the right way to save a form? In cloud there is a save button, but there is not a single version of on-prem that includes one.