Only to add historical background.
Pcbnew resolution was 1/10000 inch, one ten thousandth of an inch before v4. The resolution was not enough for tiny dimensions in mm. So rounding problems arisen or, in other words, accuracy was not optimal. Now is 1nm, enough for any manufacturer accuracy.
Athough eeschema works in a similar way, there are no problems at all. I don’t need complete accuracy for a draw. The grid is divided in 100, 50, 25 etc “lenght units” and I don’t mind if that means inches, thous, mm, km or light year. I know it is intended to be mils but I plot to pdf and then to the printer, usually with the option fit to page, what usually shrinks the final plot.