Seeing the image looks like a bleed problem. I got this problem one time and increasing the lightmap resolution solved.
Did you try increasing the lightmap to a very high valeu just to see if
something changes?
I can see in your uv all faces are separated as islands… You should try to merge some islands. Like the main branch of the tree. Theres no reason to have 1 uv island for each face.
I would say that maybe the normals of some faces are twisted… When the face are full dark…
Besides the lightmap and uv issue, I dont know what that could be…