I just noticed that when I extend the animation using the loop the first time, it throws an error:
// Error: file: D:/Program Files/Autodesk/Maya2020/scripts/others/showEditor.mel line 3567: TypeError: file D:\Program Files\Autodesk\Maya2020\Python\lib\site-packages\maya\internal\common\ae\matrix.py line 110: 'NoneType' object has no attribute '__getitem__' //
I've created more animation clips, it's always the same with each clip. What am I missing?