Recently, the SDK added the ability to add local parameters to an avatar's VRCExpressionParameters component. The SDK UI currently lets you place down more than 256 parameters, and is satisfied so long as you have at most 256 synced parameters.
I am making an avatar with 256 synced parameters, and 2 local parameters. So long as there are more than 256 parameters, the two local parameters do not respond on the radial menu, nor do they show up in the parameter list in the avatar debug overlay.
Additionally, I am doing bool->float casting in my FX animator (although I don't think this affects the behavior I'm seeing).
When things are loaded properly, the ExpressionParameters show up correctly as bools in the avatar debug overlay, but when they do not load correctly, they show up as floats like they are defined in the FX controller.