I believe there is a bug with the latest rollup function to grab the most recent date in the relation.
It probably has something to do with the dd/mm/yyyy vs mm/dd/yyyy format.
My sheet uses the dd/mm/yyyy format.
Because it’s a more logical format
When there are two flippable dates (dates that can be interpreted as mm/dd or dd/yy depending on where you live) using the dd/mm/yyyy format =
06/01/2018 (6th Jan 2018) vs 01/06/2018 (1st June 2018), it will pick up 06/01/2018 instead as the latest.