RCS scorching on Apollo 4 & 6 CMs

[Obviousman]

We were revisiting the flight of Apollo 6, and comments were made about the scorching on CM above the RCS ports.

I looked up the post mission report and it mentioned the scorching and that it was similar to that experienced with Apollo 4.

Does anyone know what caused it / what they did to fix it?

https://i.pinimg.com/originals/09/c2/59/09c2599a30aeef7606f7b5175b9ff81e.jpg