Why are these rigify auto weight paints so bad. Other parts of the body work fine, i didnt have this problem before with the same model
1 Answer
The normals are flipped on the pants. You need to turn off the Solidify modifier to see it.
To fix it switch to Edit mode, select the legs (L), and flip the normals (Alt+N Normals > Flip). In Object mode, consider to apply the scale to the model (Ctrl+A Scale). Rebind the mesh to the armature.
Last but not least, make sure the Solidify modifier is added after the Armature modifier so the Armature modifier uses the original mesh to deform.