I apologise if I've covered any answers already, but it seems to me there are several possible reasons why this might be so.
- Could the discs have initially failed at burning, and you ignored, or the software ignored any errors (Perhaps didn't verify the disc?)
- Make sure you buy always Verbatim for DL media. Even though several forms of Ritek, CMC, MBI media are all reliable, the only reliable brand of DL media are Verbatim. (You can blame the problems I've had with AOne DL media for that )
- The most common problem is for me is, other than burners not recognising the layer break (So complete and utter failure of reading second half of a burn) cheap or outdated players which struggle to play DL media. For example, my Phillips player from 2009 will play DL media (Although slow and struggles), but the same brand of player from 2004 will not play them full stop.
Although if Verbatim media really isn't your game; (Who can be 3x as much as competitors, but they are the only, in my opinion, reliable brand of DL disc) try some Traxdata DL or AOne DL because you may get some okay results granted if they don't fail outright at burning stage.