I seriously doubt this has anything to do with the burner or the media. Verifications often fail and are very unreliable. I think you're chasing a wild goose. #1 reason for playback picture breakup is over-compression. #2 cause is a player that doesn't like recordable media, or low-quality burns.
You've eliminated burn quality as an issue, although with a player that's overly picky, very small increases in errors can cause problems. But the problem is still the player in that case. Tightly packed PIF can cause some players to freeze or break up, even at low levels, but again, that's the player's problem.
Try your disc in another player. I can't stress enough that you should forget about the verification thing till you rule out the other variables. It's really very unreliable. If your disc plays well in other players, there's your solution.
If files are somehow changed, then the cause could be anywhere. The disc has been shown to be well-burned, so unreadable files is extremely unlikely. Do a transfer rate test if you have doubts. If data is corrupted in the burn process, it's happening in the system, not the burner.