This report can be a bit confusing. It can be in Forecasting more (Budget items checked) or Net Worth mode (Budget items not checked).
First column (Net Worth):
In Net Worth mode or for past dates in Forecasting mode, this column is the sum of the current account balance and any upcoming recurring items.
In Forecasting mode for future dates only, this is the sum of the current account balance, any past due recurring items, minus any non-budgeted upcoming recurring items.
Second column:
This is only used in Forecasting mode for future dates only. It is the sum of the projected budgeted spendings and any budgeted upcoming recurring items.
Third column:
This is just the sum of the first two columns, and it is the forecasted account balance, the column that's the most interesting.
The most confusing aspect is that budgeted recurring items move from the first to the second column as the date changes from past to future. The easiest way to understand is that two report mode changes as this happens, and only the first column is used for past dates.