Support got back to me with this response, sharing in case it helps~

Hi, assuming this is Quantum KCC related (we also have KCC for Fusion). So when KCC runs its update, it internally executes methods on processors (such as EnvironmentProcessor) before and after move. Because EnvironmentProcessors overrides the KinematicVelocity, calling KCC.SetKinematicVelocity() before KCC updates doesn't have any impact. You need to:

1. Remove EnvironmentProcessor and handle Gravity/KinematicVelocity/Jumping/... on your own using the KCC.SetKinematicVelocity() before KCC updates.

2. [Recommended] Create a copy of EnvironmentProcessor and modify it - so for example instead of a EnvironmentProcessor speed property you get your custom component which holds the speed and is on the KCC entity.

3. Add custom processor which overrides the velocity.

Be careful with changing EnvironmentProcessor properties (just don't do that :) ) because these are not part of the Quantum state and don't support rollback, you can easily get a desync.