Seams in the body

[Windbrand]

Does anyone know what might be causing huge seams in the body when wearing armor? Screenshots:

 

 

 

 

 

This occurs with pretty much any armor in the "BBP_armorpack" (600+mb download), but doesn't occur for most of my other mods.

I'm using the "CHSBHC" body type, which I think is the CBBE body type but with breast bounce. I thought seams occur when the upperbody doesn't join with lowerbody, eg I wear a different bodytype for upperbody than lowerbody, but the weird thing is all of these outfits are both upperbody+lowerbody, so why is there a seam?

Thanks.