Report MC-207647 doesn't include stairs, and stairs still cause the soul speed to be applied randomly and result in a "stuttering" effect.
Issue is still present in 1.17.1 and 21w41a. It doesn't applies to half-blocks anymore but still does with stairs.
Dolphins are pasive mobs, they're not supposed to hurt the player even when hit by said player.
Report MC-207647 doesn't include stairs, and stairs still cause the soul speed to be applied randomly and result in a "stuttering" effect.