The C41 developer was designed for a high speed high Iodide emulsion and the RA4 developer was designed for a slow speed fine grained emulsion. Therefore, they will perform poorly if products are cross processed using these chemistries and materials. In addition, C41 uses CD4 and RA4 uses CD3 for the color developing agent which causes additional problems.
C41 requires a different chemical bleach and fix, but a blix is barely adequate. Even longer times will not fix this problem! C41 also requires a final rinse for best stability.