brush repeats in illustrator

https://drive.google.com/file/d/1eDVSVECvruWqPeu_DHDOupsBKTbkreTT/view?usp=sharing

try this.

I'm not sure about the invisible box and pattern brushes in the past or present.. But you could make an invisible box on top of your art, then make a clipping mask out of the art and invisible box.. then use pathfinder > merge. then clean up the artwork a bit. get rid of any no stroke/no fills and ideally combine everything by color into compound paths. then group all those compound paths and you've got a really nice clean piece of art to make your pattern brush.

I recommend keeping a copy of your clipping mask and then making a duplicate before merging and doing the rest of the steps. You may find you need to do some tweaking on the exact size/position of the clipping path in order to get a seamless pattern brush. If you look closely at the one i've made, you'll see it's not perfect. But minor tweaks should yield decent results.