Changing skeletal mesh disables animation / puts character into T

When I bring in the third person blue print, the mannequin is rigged fine. I fix the blueprint issue in the lecture and it still works fine. It animates as I expect. The moment I go in and change its skeletal mesh, the model T poses and does not animate any longer. Even if I go back to the mannequin mesh, the mannequin stays T posed now. What will fix the animation of these characters when you change their mesh? In the video he just changed the mesh and things just worked. Attached image

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