The label (sticker I presume) just adds about 1mm thickness to the DVD disk. Some DVD players won't be able to handle that extra thickness. But it shouldn't cause the pixelation, though it might cause skipping or slight pauses. Try using a felt tip pen and see if that helps.
- Cleaning the disk drive with a special disk drive cleaning disk.
- A different burning program.
- Different ripping methods (if any).
- Test in another DVD player (with and without the label).
Make a note of where it stops playing on each disc. Is it the same place on each?