Trouble with calculated column by date in pivot table

[laxplayer56]

I have been having an issue since updating excel on Mac a few weeks ago. Any help adjusting settings or getting around the issue would be greatly appreciated.

On to the issue. I have a number of vendors that generate revenue every month. One of the things I do is compare how they have been doing month over month.

This has been super easy except now it doesn't want to calculate Jan 2018 to Dec 2017 anymore. This is not an issue if I run the 4th Quarter 2017, it appears the issue has something to do with the fact it now auto populates and groups by year now.

Quick example of what it should look like.

[TABLE="width: 500"]
<tbody>[TR]
[TD]Vendor[/TD]
[TD]Nov[/TD]
[TD]Dec[/TD]
[TD]% change[/TD]
[TD]Jan[/TD]
[TD]% change[/TD]
[/TR]
[TR]
[TD]A[/TD]
[TD]100[/TD]
[TD]150[/TD]
[TD]50[/TD]
[TD]150[/TD]
[TD]0[/TD]
[/TR]
[TR]
[TD]B[/TD]
[TD]200[/TD]
[TD]200[/TD]
[TD]0[/TD]
[TD]250[/TD]
[TD]25[/TD]
[/TR]
[TR]
[TD]C[/TD]
[TD]300[/TD]
[TD]200[/TD]
[TD]-33[/TD]
[TD]300[/TD]
[TD]33[/TD]
[/TR]
</tbody>[/TABLE]

It is no longer calculating that last column. Thanks for your help