The tail doesn't seem to be animating, it just sticks straight out.
Viewing post in Ultimate μ2 (VRC / Blender) comments
Your SDK version might be out of date. This can cause earlier versions of physbones scripts to break if you don't update. You can also reassign it by copying the values, removing the script on the base of the tail, adding the physbone script back, and pasting the same values.
If your system settings are low, or are using this release on a non-PC platform, that can lead to additional issues.