Using YNAB data to create cash flow statement

I wonder if someone can help me figure this out...

im trying to do a cashflow statement at the end of each month using my ynab spending data. But I can't get it to reconcile.

I feel like it should work like this...

I look at ending balances on all my categories in August. That is my "Beginning cash"

I then look at reports and i add Income, and subtract expenses, that gives me "Ending Cash".

Shouldn't this "Ending Cash", equal the total of the ending balance on all my categories in September?

it's been off each month and I can't figure out why. Sometimes a few dollars sometimes more. I assume it maybe has to do with how i'm inflowing money or categorizing stuff or how credit card balances are treated... but haven't figured out exactly why so that I can adjust my spreadsheet to be accurate