Spline points are deleted from the Spline component after adding them in Python and then moving them in the scene.
Tested in 4.21.2 (CL - 4753647) 4.22.3 (CL - 7053647), 4.23.0 (CL - 8386587), 4.24 (CL - 8506911)
Expected: The new spline point is made and persists
Result: The new spline point is removed
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-79935 in the post.