So I tried this out today and it turns out Azureblight causes small stutter whenever stacks are applied to multiple people (e.g. Stampede, Hurricane, Deadly Cloak etc - every Blight Seed source seems to cause this lag). The more people you hit/the more stacks you're generating, the more lag you get.
I tried disabling addons, turning down particle systems, changing the other sets etc and nothing seems to fix this issue.
I'd like to note that I have/had (haven't tested it yet in this patch) a similar issue with Thurvokun, where it'd cause some extreme FPS drops whenever the effect went out and applied its debuffs to someone.