I noticed during Edit that my SuperTile appeared unchanged after several attempts to add a String variable, which happened to be empty (no Value set). So I revisited the var’s definition page and assigned it a temporary value.
Suddenly the SuperTile showed all 3 copies of the String variable, which I was free to move, delete, etc. They must have been “there” but “invisible” before?
Not sure if this qualifies as a bug, expected behavior, or what, but for me it was all rather unexpected. My original intent was simply to create an empty box to act as a placeholder for a variable which would be assigned values (by Rules) later.