If the two slicers come from the same Date column, both periods do not intersect each other and you get a filter without dates.
Possibly there are better solutions but one of them would be to use a Harvester Filter (Creating an additional table containing a copy of the date column unrelated to the model, aka Disconnected Tables)
Before moving on to the next part you can verify that the filter contains the same dates but since it is a disconnected table, it does not filter the model, yet
For the [Profit given Date Slicer 1] you can use the original measure
For the [Profit given Date Slicer 2] you must change the filter to:
DATESBETWEEN(
'Dates'[Date],
MIN(HarvestingDates[Date]),
MAX(HarvestingDates[Date])
)