Why is my formula returning a zero ?

Hi,

I have a fomuala that randomly generates a value, that is taken from another list.

The excel sheet will not generate any new values past the 1st June.

When I intially past the formula in, it generates a value. After this, if I click on a cell past the 1st June, the cell returns a "0" rather than adate.

Is there any obvious cause of this ? I am using Microsoft Excel online

The formula is

=INDEX($BB:$BB,AGGREGATE(15,6,ROW($BB$8:$BB$43)/(COUNTIF($M124:$AW124,$BB$8:$BB$43)=0)/(COUNTIF($B124:F124,$BB$8:$BB$43)=0)/(COUNTIF($G$2:$G123,$BB$8:$BB$43)<$BG$52),RANDBETWEEN(1,COUNT(1/(COUNTIF($M124:$AW124,$BB$8:$BB$43)=0)/(COUNTIF($B124:F124,$BB$8:$BB$43)=0)/(COUNTIF($G$2:$G123,$BB$8:$BB$43)<$BG$52)))))



Thanks.