Custom buttons got a little bit of a make-over in the 2016 version, and this is the case whether you have switched to the new version of not…
BEFORE, each custom button would be a visible button in the area you selected (List view, View or Edit)
NOW, they are together in a drop down list with ONLY the name of the first button showing.
Also, for buttons placed in the list view, in the new version you must now select at least one record before the buttons become visible:
