Excel ranges typed in with two periods

Until recently, I was able to specify summing all the cells in column a by using

=sum(a..a)

which upon pressing enter would automatically convert to

=SUM(A:A)

Is there a reason this no longer works? Is there a setting I’m missing that got changed on me?

I’m experiencing this on Excel for Office 365 MSO (16.0.11328.20478) 32-bit.