DVD's come in dual and single layer.
Check to see if the DVD's that play are all Single layer.
Some drives at the end of life(or defect) start to have problems seeing the second layer(done with red light[would guess it is an led] that lets it see the other layer, i have seem this "light" just stop working) on dual layer discs and will still play single layer just fine.
If a disk is under about 4.5 gigs its single layer up to about 8 or so will be dual layer so if ALL working discs are single layer, that may be the issue.