Not enough disk space (batch export) strange behavior!

just wanted to export a 67 audio tracks+1 instrument and i got the “not enough disk space” message.
i checked and there is a lot of space, check other things as well but the same.
then i did batch exports in random number of tracks, 15 then 10 then 20 and so on, only this way i could export the all tracks, but not in one go.
any thoughts what can cause this ?