It would be nice to know where the leak is coming from, like from all areas or mostly leg or back. It's hard when small & poop is very liquid to prevent all leaks, certain folding techniques also help, particularly when using prefold or flatfolds. The carrier can make it more likely because the position of the baby is such as to put pressure right in the area you hope is going to contain the poop, and so it forces the poop to redirect it's movements, sometimes out the legs or up the back.
I have always had an ergo, and I have cloth diapered 3 kids in it. I have used different methods on diapering all along, everything from all in ones to flatfolds with wool or pockets or all in 2s. There are a ton of styles. Some for sure are more prone to leaking than others. The one thing that is awful in a leak is when it happens on things you don't want to have to wash so often, like a carrier.
What is the type of diaper being used? Is it smooth? I had some lovely soft organic cotton bamboo that was exceptionally smooth. We were having lots of leaking issues so I tried cutting up a small baby towel & would lay in a portion of that with the loopy side facing the baby & it fixed it immediately. The poop had nothing to grip it seems, so when she would go, it would just flow, rather than be grabbed & contained. It's possibly something as simple as that.