I've been doing some manual unwrapping when meshes looked like a circle full of triangles in the uv layout, I would add some cuts to split it up into pieces until pressing `u` would no longer show black faces. Then I would start looking at the island edges and how to stitch back together(maybe looking at and using 3D view to get the right shape).
When doing the above, I would have an island that grows bigger every time I unwrap after welding the smaller island to it. At first it's not a problem, but then it starts to get too big, bigger than a udim tile, sometimes bigger than all udim tiles. I have to run pack command to fix it. Maybe this has been fixed since I was on 0.10.9, only updated recently.