Seamless loop animation
I not know how do this with AE animation software but I do this in Blender:

                
            

Basic theory (see picture) for real camera or software:

• Want repeat image every n animation frames

• Assume camera view is w × h pixels

• For camera view w pixels wide, minimum need draw picture wide 2w pixels wide

• Copy picture two times and put left/right each other (draw left and right edge of image for can't see edge)

• Shift picture -w pixels for first animation frame relative to camera left edge

• Step size for each animation frame is ∆s = w/n

• Image position = ∆s*(animation frame number mod n), means at every n animation frames shift image back -w pixels (return to start position)

• Use linear interpolation for image position (need select this for Blender)

• Use repeat cycle (for Blender)


Blue dot show shift for each animation frame

If image is wider than camera view (R ≥ w):

• shift picture -R pixels for start animation frame

• step become ∆s = R/n

• shift image back -R pixels

Reverse Direction

• Shift picture 0 pixels for first animation frame relative to camera left edge

• Step for each animation frame is ∆s = –w/n (∆s = –R/n for image R ≥ w), negative direction