The problem I had was that although the source data was correctly formatted as 'date' dd/mm/yyyy, the pivot table placed (for example) 22/05/2019 between 16/05/2019 and 17/05/2019. This data was visible in the pivot table, but in the wrong place. In addition, the Pivot chart refused to show that data for that date even though the 'Date' filter allowed it to be selected.
In my case, I had to:
From the Pivot Chart,open the 'Date' Filter menu.
select the 'Sort Oldest to Newest' option.