When the audio starts skipping towards the end of a CD-R disc, this may be caused by a combination of different circumstances. When music files are burned onto a CD-R disc, they are burned from the center out towards the edge. This means that the data towards the edge of the disc will be spaced further apart than the data near the center. In addition, heat is generated when the disc is playing. The longer the disc is playing, the hotter it will become. This heat can slightly alter the physical characteristics of the disc and make track recognition more difficult. For these reasons, it is possible that audio skipping may occur on tracks recorded towards the end of the disc. This issue may be more evident on discs with over an hour of recorded music.
NOTE: The speed at which the CD-R disc was burned may also have an impact in regards to this issue as well as the type and brand of CD-R disc being used. You may want to try playing different types or brands of CD-R discs that have been recorded at different speeds.