Hi again! :D
This one is hard to explain, so I've made a video.
As my English speaking is probably not very good, I add here what I spoke in the video:
"If I try making a looping animation for the white box, and the keyframes I make are on the zero second and in the middle of the time duration, everything's fine. I don't even need to add a frame at the end of the time for it to loop, which is really nice. But if I try to make another similar animation with a bit of delay, I cannot make it to loop like the first one."
So, my suggestion would be adding a loop option for each track. If checked, it would make the animations to loop seamlessly :)
A way for make it work could be that the program would "create invisible keyframes", those keyframes would be outside of the timeline. In my example, for the blue box, it would create a keyframe "X Position = 50px" at -0.3 seconds and another one "X Position = -50px" at 1.02 seconds.
I hope it makes sense, and I hope you like the idea! :)