Setting Key Interpolation for a point on a curve to Auto behaves differently than it did in UE4. The results are more akin to the User Interpolation with flat tangents.
The handles line up with the line between the 2 points(see attachment UE4_AutoCurve)
The handles form a flat tangent like the User Interpolation(see attachment UE5_AutoCurve)
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-146356 in the post.