This happens with 2.5 and I saw it in one export file from 2.4 also.
Some players name-field is completly empty in the export file. It is not on the stats tab. This happens when exporting the stats or the tournament data.
When I sort the stats by an other collumn, two other names disappear. There are always 2 names missing but which two changes by the sorting. I could not find any system there. Weird!
CSV exports from the same data work fine.