Hi,
I’ve been digging around why SSR in UE4 is so noisy, and I have found the culprit:
SSR in UE4 has temporal interpolation implementation, which is supposed to be enabled by default according to the command help, but is wrongly set to 0 for all new projects. Once you set it to 1, you should observe drastic reduction in noise and improvement in quality of SSR.
Have fun! 