  The second magnetization peak (SMP) appears in most superconductors and is
crucial for the understanding of vortex physics as well as the application.
Although it is well known that the SMP is related to the type and quantity of
disorder/defects, the mechanism has not been universally understood. In this
work, we selected three stoichiometric superconducting
RbCa$_2$Fe$_4$As$_4$F$_2$ single crystals with identical superconducting
critical temperature $T_c$ $\sim$ 31 K and similar self-field critical current
density $J_c$, but with different amounts of disorder/defects, to study the SMP
effect. It is found that only the sample S2 with a moderate disorder/defects
shows a significant SMP effect. The evolution of the normalized pinning force
density $f_p$ demonstrates that the dominant pinning mechanism changes from
weak pinning at low temperatures to strong pinning at high temperatures. The
microstructure study for sample S2 reveals some expanded Ca$_2$F$_2$ layers and
dislocation defects in RbFe$_2$As$_2$ layers. The normalized magnetic
relaxation results indicate that the SMP is strongly associated with the
elastic to plastic (E-P) vortex transition. As temperature increases, the SMP
gradually evolves into a step-like shape and then becomes a sharp peak near the
irreversibility field similar to what is usually observed in low-temperature
superconductors. Our findings connect the low field SMP of high-temperature
superconductors and the high field peak of low-temperature superconductors,
revealing the possible universal origin related to the E-P phase transition.
