Ah I see now. This is a bug that happens because some of your physics constraints have an update rate of 120 FPS. We'll get it fixed in 4.2.08-beta. Sorry for the trouble!
A couple comments on your project: You have 15.5k keys to loop the animation. If you export GIF, APNG, or video, you can choose Animation repeat
, which may be easier depending on what you are doing with the export. You have 194 physics constraints for pretty simple movement. It probably would have been easier to just key the movement, but the constraints could make sense if you plan for other animations or want it to be dynamic.