This is somewhat alarming, but not completely unexpected.
Both Nec ND2500A and 2510A seem to have issues with reading back some of their own burns, regardless of media quality, firmware or burn speed (* often these “unreadable” discs read back perfectly in all other drives).
I was hoping the problem would have been fixed for ND3500, but your posts suggest otherwise.
I hope other people could chime in, if they have problems reading back burns done with their ND3500 burner.
In all fairness, it must be stated that there seem to be many people who are not suffering from this kind of problem on their Nec ND25x0 units, although some unlucky ones are.
According to some, NEC is aware of the reading problems with 25x0 series, but it remains to be seen if it’ll get fixed.