This is the output of my 2016 MBP keyboard when I alternately press the x and return keys. When there is an empty line the x key did not register. When there is a xx in a line, the key registered twice.

mbpkeyboard.txt

x
x
x
x
x

x
x
x
x
x
x
x
x
x
x
x
x

x
x
x


x

x
x





x

x



xx
xx
x

x
x
xx
x
x
x
xx

x

x
x

x


x

x
x


x


x
x

x

x






xx

x
x
x
x
x
x
x
x
x
x
xx


x

x

x
x
x
x
x



x
x
x




x

xx

x
x

x
x

x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x

x
x


x
xx
x
xx







x

x
x
xx
x
x
x
x



x


x
x

x
x
x
x
x
x