I'm glad I saved this as a project :)
80 bpm, no problems. Looped umpteen bazillion times.
100 bpm, same. No problems.
120 bpm, same again. No problems.
Have you started over with a fresh project to see what happens?
Sounds to me like you're experiencing buffer underruns, dropouts, whatever, and your audio driver isn't dealing with it very well. Or your audio driver is just flaky.