Thank you for your answer.
I modeled DCB under mix mode I & III loading condition. I attached the geometry here.
Indeed, the problem is not limited to the value of edges merely.
I have attached here the distribution of mode I and mode III energy release rate. The fracture tool cannot obtain energy release rate at the edges and center of the specimen for both mode I & III when I use a refined mesh. However, the nodal vcct works perfect. (Nodal VCCT: First, extract the nodal force and displacement and calculate the energy release rate myself)
In my opinion, this is a postprocess error, because I have to arrange(sort) the data to calculate the energy release rate myself.
I hope you can help me to solve this problem. My colleagues ask me to switch to ABAQUS instead of working with ANSYS to analyze the fracture behavior.