Why is my character moving out of place in the middle of the blend?

The Pelvis is matched so when they’re not blended, the 1st clip ends where the 2nd clip begins. But when blended, the mesh moves out of place then back. It happens right in the middle of the blend. What am I missing?

The overlap that is happening between two animation is likely the cause of it. You can try moving the interpolation graph that you see between the blending animation to fix that.