CPU Usage Only at 9% During "Building Light Cache"

[hrigsby]

I have a memory heavy file that I'm trying to render out and it suddenly has decided to stop working. My machine has a 16 thread processor and 128 GB of RAM. It starts off normally, but right after it starts "Building Light Cache" the CPU usage drops to 9% (one core essentially) and the estimated time to complete jumps up to multiple hours instead of less than 3 minutes.

I had this issue before when my computer had less RAM, but then it was bouncing off of the upper limits and throttling the CPU. Now it's only using 30% of the RAM and still throttling down for some reason. Any ideas what is wrong?

EDIT: For starters, I've adjusted the Dynamic Memory Usage from 0 (my usual setting) to 127999 MB, which didn't help. I've also cut off some of my FB objects just to see if I was somehow overloading the scene, but that didn't help either.

I also tried replacing Light Cache with Brute Force, and got the same result (just during a prepass rather than during the light cache build.

[^Lele^]

take a look here, it may help.

[hrigsby]

take a look here, it may help.

I checked it out. Good tips to incorporate, but I'm not bouncing off of the memory limit with this file I don't believe. I've been fine for previous test renders and the only thing I did was create a new camera view between those renders and now.

[^Lele^]

It'd be great if you could share the scene (or offending part thereof) with support, then.
You may link them this thread, if you want.

[Vizioen]

Does merging in a new scene help? I've had the LC act up sometimes for no apparent reason, computer reboot or scene merge helped most of the time. If not than I'd suggest merging systematically until you find the culprit that messes with the LC.