Hello,
I think that your column 'date loan start' that belong to loans table is following up format like 'dd/mm/yyy hr:mn:sc' with 'hr:mn:sc' values different than '00:00:00' nevetheless the Date column that belong to dimeDate table follow similar format 'dd/mm/yyy hr:mn:sc' but with the only difference that 'hr:mn:sc' values have '00:00:00' as value.
make sure to format in power query column of 'date loan start' to date only as well as Date column that belong to DimDate