Occurred consistently on Rebug 4.84.2 REX and Evilnat 4.88.2. Both with Cobra disabled obviously.
I tested back and forth several times between those two CFWs (with a few clean installs, no less) and I always could reproduced this issue. It didn't matter whether Restore File System being triggered automatically or manually. The blackscreen freeze always occurred after RFS completed its process and reboots the console.

I already pulled my HDD and plugged it on my PC then checked it with Harddisk Sentinel and HDD Regenerator and found no problems. This issue doesn't occur when I'm using Cobra. As an additional info, on Evilnat 4.88.2 the blackscreen freeze also occurs when I use the reboot LV2 from the CFW menu.

I hope you can help me because Mamba performs better in my console. Using Cobra makes Diablo 3 stuttering like crazy but with Mamba the stutters are very minimal and the temps are lower as well.