Far as I can tell, the VampireRun walkstyle is somehow hard-coded to having the Vampire Trait. Can't seem to track down in what way though. I figured maybe it's to do with the default vampire walkstyl...
The reason you don't always see the highest priority walkstyle is that the Sim accounts for distance, and might choose a slower walkstyle. You need to look at the tuning on the Sim to override those distances for specific styles (e.g. the Grim Reaper never accounts for distance, and always uses the floating walk).
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