I've just been trying out multi-frame rendering with a small sequence that has a single instance of Keylight 1.2 on some video footage.
I initially tried it just RAM previewing and found that the time to render was the same for single and multi-frame rendering. I could see that multi-frame was working and CPU utilisation was much more. Info said that at some points, 8 frames were rendering,
So then I tried a proper output from the AE render queue. I tried both single and multi-frame. The single took 31s and then the multi-frame took 54s! I had purged memory and disk cache between each attempt. I was saving as ProRes 422 in Qucktime wrapper.
Specs - Windows 10 Pro 10.0.19043
Intel i7-7700K 4.2GHz 4 core
ASUS Maximus IX hero
NVME system and data drives
AE 22.1.0 (build 1)
Happy to share project comps if needed.
I've had to roll back to 22.0 due to the system font issue and it seems to be behaving now - multi-frame render is quicker but by varying amounts. When the bug fix version drops later, i'll try that too.