Good question! In radiation pressure the fact that the charges radiate energy isn’t included, it’s just the change in momentum due to to radiation being absorbed or reflected that produces a force. In radiation reaction the charges are accelerated and decelerated by the electric field of the light. Classical electrodynamics says the electrons must give off em radiation, and so must lose energy in the process, so must be an additional force associated with this emission. Physicists such as Dirac looked at classical radiation reaction in the early 20th century, but I don’t think it’s effect has been observed in the interaction of electrons with light before. At very high electron energies and/or laser intensities the classical description of radiation reaction should break down.