@Brad said:
I am using Pro Tools 2018.4, what version are you on? Not seeing this on my system. Have you changed any of the performance settings in SD3 (CPU Cores for example)?
Is it a specific preset or kit, or is it happening consistently with any preset or kit. It’s an oddity that it only happens when stopping playback.  

This is 2018.4. The audio is on a separate drive from the OS. It’s set to use one CPU. There are four available, but if I try to add more, the performance seems to go completely haywire so I leave it at 1. Don’t AAX plugs automatically get distributed across the CPUs by Pro Tools? I’ve never had a plugin that required you to specify how many CPUs to use. This seems like an odd thing to request from a user. I have it set to load the cache for the entire kit (24GB of RAM available) so it doesn’t spike whenever it loads a cymbal crash for the first time.

I’ve tried different kits, including both SD3 and EZDrummer expansions. Some kits seem to spike a bit more than others, but they all have a big spike, and only when stopping playback from the DAW. I don’t have any issue using EZKeys, which is usually quite CPU efficient.

For the most part, other plugins (mostly Waves) barely move the needle. The only other plugin that I struggle with is the Abbey Road Plates, which is a legendary CPU hog, but even that one doesn’t spike to 100 percent.