How to make a seamless loop on GIF

To make your GIF loop seamlessly, ensure the first and last frames match or use a fade transition. You can also adjust the frame rate, optimize the GIF with tools like Photoshop or EZGIF, and reduce resolution or simplify the animation to stay under 10MB.

You posted in the Photoshop forum but have now confirmed you are using After Effects. I've moved your post to the after effects forum.

To make the background seamless either construct it so that all elements start and end at the same point or, consider repeating each element and fading it in and out, so that as one fades out another fades in. It will take the eye away from a sudden jump.

I'm guessing that you would need to use Pattern Preview and Offset.

Another way would be to mirror thje graphic vertically.  

Testing with this graphic

If I check it with View > Pattern Preview

It actually doesn't look too bad vertically

Flipping it looks better though

I think Jesus Rameriz did a Pattern Preview video recently

Yep. Here you go

Arfe you OK making the frame animation from there?