hi there, I hope I'm posting this in the correct part of this forum.

short introduction: I've started working with 3D art a few years ago. I'm currently working with Poser 11 pro and blender 2.81 I've learned how to model, UV map and texture 3D assets and wanted to learn how to create some rigs in blender. So far, I've managed to rig a few simple items to use in poser, like a rope, a swing, a crocodile like tail and a sci-fi rifle, so I can say I do know the basics about rigging and weightmapping, but that's basically it. I don't know much about remeshing and whenever I think I finally got it, a month later I learn that my last mesh was far from optimal to rig ^^'

my problem: I want to learn how to model and rig more complex stuff like faces and whole characters, but everytime i sculpt for example a face and port it over to poser, it doesn't work properly. I set the Skinning method to "poser unimesh" in order to be able to add subdivision levels, but in some areas, the mesh just breaks appart and i have no idea why.

here's a picture of a sort of swamp imp. the fins on the top of the head as well as the tongue and the lower jaw have all bones (plus the head of course). when I move the tongue, everything works fine. moving the fins is fine in some areas, in some not. closing the jaw though breaks the mesh in two halves...

what am i doing wrong ? thanks for any advice

PS: I'm exporting from Blender as FBX (I don't change any options besides activating "selected objects" so only my selection is being exported. i select the rig and the mesh, nothing more)