Difference From in Pivot Table skipping first day of month

EDIT: I've since decided to go in a different direct with my file rendering this post "not needed", however, if there's a simple solution, I'd still love to hear an answer. Thank you

Hello,
I have a Pivot table with three columns. Date, Total Number and Change
The problem is, the Change field (on the righthand) is calculated using "Difference From" and "Previous" (Date), yet for each 1st of the month (ie: May 1 shown below, April 1, Mar 1 are all blank as well), the field is blank. My data comes from Power Query and is formatted as whole numbers, so that shouldn't be the problem. I can't even make the blank value show as 0. When I hover over the empty cell it says "Value: No value".

30-Apr 3133235 77806
1-May 3217821
2-May 3309563 91742
3-May 3390732 81169

It should show 84,586.

Any help would be greatly appreciated!

I can see the same behaviour in a standard PT BUT only for the first date where there is no preceding date. Subsequent changes of month continue to show a change day by day.

Are you able to upload the workbook?